.     .       v  ..': 


uty?  1.  %.  ?4tU  Ktbraru 


North  (Carolina  S>tate  (Uollrgr 

QH96 


i« 


S00701131    D 


21978 

This  book  may  be  kept  out  TWO  WEEKS 
ONLY,  and  is  subject  to  a  fine  of  jfj0& 
CENTS  a  day  thereafter.  It  is  due  on  the 
day  indicated  below: 


!5Apr'58F 


«M/V 


« 


DE08Q  9  | 

5M— F45— Form  3 


* 


** 


m 

1994 


\ 


SEASONAL   CHANGE* 


The  view  is  from  West| 


RENWICK   MARSH    AT    ITHACA 


UTUMN 
FIRES 


Winter 

EEZING 


ing  across  the  valley. 


THE  LIFE  OF  INLAND 
WATERS 


An  elementary  text  book  of  fresh-water  biology 
for  American  students 


By 
JAMES  G.  NEEDHAM 

Professor  of  Limnology  in  Cornell  University 
and 

J.  T.  LLOYD 

Instructor  in  Limnology  in  Cornell  Unix  srsity 


191b 

THE   COMSTOCK  PUBLISHING   COMPANY 

ITHACA,  NEW  YORK 


COPYRIGHT,    1915 
COPYRIGHT,    1916 

THE   COMSTOCK    PUBLISHING   CO. 


PREFACE 

IN  THE  following  pages  we  have  endeavored  to  present  a 
brief  and  untechnical  account  of  fresh-water  life,  its  forms, 
its  conditions,  its  fitnesses,  its  associations  and  its  economic  pos- 
sibilities. This  is  a  vast  subject.  No  one  can  have  de- 
first  hand  knowledge  in  any  considerable  part  of  it.  Hence, 
even  for  the  elementary  treatment  here  given,  we  have  borr 
freely  the  results  of  researches  of  others.  We  have  selected  out 
of  the  vast  array  of  material  that  modern  limnological  studies 
have  made  available  that  which  we  deem  most  significant. 

Our  interests  in  water  life  are  manifold.  They  are  in  part 
economic  interests,  for  the  water  furnishes  us  food.  They  are 
in  part  aesthetic  interests,  for  aquatic  creatures  are  wonderful  to 
see,  and  graceful  and  often  very  beautiful.  They  are  in  part 
educational  interests,  for  in  the  water  live  the  more  primitive 
forms  of  life,  the  ones  that  best  reveal  the  course  of  organic  evolu- 
tion. They  are  in  part  sanitary  interests;  interests  in  pure 
water  to  drink,  and  in  control  of  water-borne  diseases,  and  of 
the  aquatic  organisms  that  disseminate  diseases.  They  are 
in  part  social  interests,  for  clean  shores  are  the  chosen  places  for 
water  sports  and  for  public  and  private  recreation.  They  are 
in  part  civic  interests,  for  the  cultivation  of  water  products  for 
human  food  tends  to  increase  our  sustenance,  and  to  diversify 
our  industries.  Surely  these  things  justify  an  earnest  effort  to 
make  some  knowledge  of  water  life  available  to  any  one  who  may 
desire  it. 

The  present  text  is  mainly  made  up  of  the  lectures  of  the  senior 
author.  The  illustrations,  where  not  otherwise  credited,  are 
mamly  the  work  of  the  junior  author.  Yet  we  have  worked 
jointly  on  every  page  of  the  book.  We  are  indebted  for  helpful 
suggestions  regarding  the  text  to  Professors  E.  M.  Chamot,  G.  C. 
Embody,  A,  H.  Wright,  and  to  Dr.  W.  A.  Clemens.  Miss  Olive 
Tuttle  has  given  much  help  with  the  copied  figures. 


21978 


10  Preface 


.  when  a  course  in  general  limnology  was  first  estab- 
i     rnell  University,  we  have  been  associated  in  develop- 

n  outline  of  study  for  general  students  and  a  program  of 
j.     The  text-book  is  presented  herewith:     the 
ical  exercises  are  reserved  for  further  trial  by  our  own  classes; 
they  are  still  undergoing  extensive  annual  revision. 

The  liniitati.  >ns  of  space  have  been  keenly  felt  in  every  chapter; 
ially  in   the  chapter  on  aquatic  organisms.     These  are  so 
us  and  so  varied  that  we  have  had  to  limit  our  discussion 
,  ,f  ti,  ,  ,Ups  of  considerable  size.     These  we  have  illustrated 

in   the  main   with   photographs  of   those  representatives  most 
commonly  met  with  in  the  course  of  our  own  work.     Important 
S  are,  in  some  cases,  hardly  more  than  mentioned;  the  stu- 
dent will  have  to  go  to  the  reference  books  cited  for  further  infor- 
■'■  m  concerning  them.     The  best  single  work  to  be  consulted 
in  this  connection  is  the  American  Fresh-water  Biology  edited  by 
Ward  and   Whipple   and   published   by  John  Wiley  and  Sons. 
Our  bibliography,  necessarily   brief,   includes  chiefly   American 
rs.     We  have  cited  but  a  few  comprehensive  foreign  works; 
the  reference  lists  in  these  will  give  the  clue  to  all  the  others. 

It  is  the  ecologic  side  of  the  subject  rather  than  the  sys- 
tematic or  morphologic,  that  we  have  emphasized.  Nowadays 
there  is  being  put  forward  a  deal  of  new  ecologic  terminology 
t<  it  which  we  have  not  discovered  any  good  use;  hence  we  have 
omitted  it. 

Limnology  in  America  today  is  in  its  infancy.  The  value  of 
its  past  achievements  is  just  beginning  to  be  appreciated.  The 
fits  to  come  from  a  more  intensive  study  of  water  life  are 
just  beginning  to  be  disclosed.  That  there  is  widespread  interest 
is  already  manifest  in  the  large  number  of  biological  stations  at 
which  limnological  work  is  being  done.  From  these  and  other 
kindred  laboratories  much  good  will  come;  much  new  knowledge 
iter  life,  and  better  application  of  that  knowledge  to  human 
welfare. 

James  G.   Needham. 
J.  T.  Lloyd. 


CONTENTS 

CHAPTER   I 

Introduction 

The  study  of  water  life  p.  14.  Epoch-making  events:  the  invention  of  the 
microscope,  p.  15.  The  publication  of  the  Origin  of  Species,  p.  17.  The 
discovery  of  Plancton,  p.  18.  Agencies  for  the  promotion  of  the  study 
of  Limnology,  p.  20.     Biological  field  stations,  p.  23. 

CHAPTER   II 
The  Nature  of  Aquatic  Environment 

I.  Properties  and  uses  of  water:  transparency,  etc.,  p.  26.  Stratification, 
p.  31.     The  content  of  natural  waters,  pX^o^ 

II.  Water  and  land,  p.  55. 

CHAPTER   III 
Types  of  Aquatic  Environment 

I.  Lakes  and  Ponds:  Lakes  temporary  phenomena,  p.  60.  The  Great 
Lakes,  p.  63.  The  Finger  Lakes,  p.  64.  The  lakes  of  the  Yahara  valley, 
p.  66.  Flood  plain  lakes,  p.  67.  Solution  lakes,  p.  68.  Depth  and 
breadth,  p.  71.     High  and  low  water,  p.  74. 

II.  Streams:  Gradient  of  stream  beds,  p.  77.  Ice  in  streams,  p.  80.  Silt, 
p.  84.     Current,  p/£ft.     High  and  low  water,  p.  87. 

777.  Marshes,  swamps  and  bogs:  Cat-tail  marshes,  p.  91.  Okefenokee 
Swamp,  p.  93.  Climbing  bogs,  p.  94.  Muck  and  peat,  p.  95.  High 
and  low  water,  p.  (q6^) 

CHAPTER   IV 
Aquatic  Organisms 

I.  Plants:  The  Algae,  p.  101.  Chlorophylless  water  plants,  p.  139.  The 
mossworts,  p.  146.     The  fernworts,  p.  149.     The  seed  plants,  p.  151. 

II.  Animals.  Protozoans,  p.  159.  The  lower  invertebrates,  p.  163.  Arthro- 
pods, p.  183.     Insects,  p.  195.     Vertebrates,  p.  231. 


j  2  Content: 


CHAPTER  V 
Adjustment  to  Conditions  of  Aquatic  Lif? 

I.  Individual  Adjustment,  p.  242.      1.     To  open  water:      Flotation,  p.  243. 

mining,  p.  249. 

2.  Adjustment  to  shore  life,  p.  251.      Avoidance  of  silt,  p.  252.     Bur- 
r  wing,  p.  254.     Shelter  building,  p.  257.     Withstanding  current,  p.  258. 

3.  Adjustment  of  life  cycle:     Encystment,  p.  261.     Winter  eggs,  p.  266. 

4.  Readaptation    to  aquatic  life:      Plants,    p.    270.       Animals,  p.  273 

II.  Mutual    Adjustment,    p.    282.        1.      Insectivorous     plants,     p.    283. 
2.     The  larval  habits  of  river  mussels,  p.  286. 

CHAPTER  VI 

Aquatic  Societies 

J.     Limnetic    Societies.       1.     Plancton,    p.    294.       Seasonal  range,   p.  302. 
Plancton  pulses,  p.  305.     Distribution  in  depth,  p.  307. 
2.     Xecton,  p.  313. 

II.  Littoral  Societies.  I.  Lenitic  Societies,  p.  315.  Plants,  p.  318.  Ani- 
mals, p.  324.  Spatial  relations  of  lenitic  animals,  p.  326.  The  life  of 
typical  lenitic  situations,  p.  333.  Of  ponds,  p.  334.  Of  marshes,  p. 
341.  Of  bogs,  p.  348.  Of  stream  beds,  p.  356. 
2.  Lotic  societies,  p.  363.  Plancton  gathering  forms,  p.  364.  Free 
living  foragers,  p.  368.     Shelter-building  foragers,  p.  371. 

CHAPTER  VII 
Inland  Water  Culture 

I.  Aboriginal  water  culture,  p.  377. 

II.  Water  crops:  Plants,  p.  379.  Animals,  p.  382.  Fish  culture,  p.  384. 
The  forage  problem,  p.  387.  Staple  forage  crops,  p.  389.  The  way 
of  economic  progress,  p.  399. 

III.  Water  culture  and  civic  improvement,  p.  401.  Reclamation  enterprises: 
Waste  wet  lands,  p.  402.  Reservoirs,  p.  403.  Scenic  improvement, 
p.  404.     Private  water  culture,   p.  406.      Swamp  reservations,  p.  408. 

BIBLIOGRAPHY   p.  413 

List  of  initials  and  tail-pieces p.  420 

Index  p.  421 


ZKTT  UBtOft 
State  Cotfem 


CHAPTER  I 

NTROBUCTION 


INDIANS  GATHERING  WILD  RICE,  N.  MINNESOTA 

HE  home  of  primeval  man  was 
by  the  waterside.     The  springs 
quenched  his  thirst.     The  bays 
afforded    his    most    dependable 
supply  of  animal  food.     Stream- 
haunting,     furbearing     animals 
furnished    his    clothing.        The 
rivers  were  his  highways.    Water 
sports  were  a  large  part  of  his  recreation;    and  the 
glorious  beauty  of  mirroring  surfaces  and  green  flower- 
decked  shores  were  the  manna  of  his  simple  soul. 

The  circumstances  of  modern  life  have  largely 
removed  mankind  from  the  waterside,  and  common 
needs  have  found  other  sources  of  supply;    but  the 

13 


j  ,  Introduction 


primeval  instincts  remain.     And  where  the  waters  are 

clean,  and  shores  unspoiled,  thither  we  still  go  for  rest, 

and  refreshment.     Where  fishes  leap  and  sweet  water 

lilies  glisten,  where  bull  frogs  boom  and  swarms  of 

May-flies  lmwr,  there  we  find  a  life  so  different  from 

|  of  OUT  usual  surroundings  that  its  contemplation 

is  full  of  interest.     The  school  boy  lies  on  the  brink  of  a 

pool,  watching  the  caddisworms  haul  their  lumbering 

bout  on  the  bottom,  and  the  planctologist  plies 

his  nets,  recording  each  season  the  wax  and  wane  of 

generations  of  aquatic  organisms,  and  both  are  satisfied 

irvers. 

The  study  of  water  life,  which  is  today  the  special 

vinee  of  the  science  of  limnology*,  had  its  be^nning 

in  the    remote    unclironicTe^jast-      LimnologyTs"  a     ^ 

m<  m [ern  name ;   1  >ut  many  limnological  phenomena  were 

km  >wn  of  old.     The  congregating  of  fishes  upon  their 

spawning  beds,  the  emergence  of  swarms  of  May-flies 

from  the  rivers,  the  cloudlike  flight  of  midges  over  the 

marshes,  and  even  the  "water  bloom"  spreading  as  a 

filmy  mantle  of  green  over  the  still  surface  of  the  lake — ■ 

such  things  could  not  escape  the  notice  of  the  most 

ual  observer.     Two  of  the  plaguesofEgypt  were 

limnological  phenomena;    the  plague  "of  frogs,  and  the 

plague  of  the  rivers  that  were  turned  to  blood. 

Such  phenomena  have  always  excited  great  wonder- 
ment.    And,  being  little  understood,  they  have  given 
to   most   remarkable   superstitions.!     Little   real 

*Limn<>s  =  shore,  waterside,  and  logos  =  a  treatise:     hydrobiology. 

fThe  f<  'Ik  lore  of  all  raees  abounds  in  strange  interpretations  of  the  simplest 

limnological  phenomena;    bloody  water,  magic  shrouds  (stranded  "blanket- 

pirits  dancing  in  waterfalls,  the  "willo'  the  wisp"  (spontaneous  com- 

rsh  gas),  etc.     Dr.  Thistleton  Dyer  has  summarized  the  folk  lore 

last  mentioned  in  Pop.Sci.AIontlily  19:67,  1881.     InKeightly's 

Fairy  Mythology,  p.  401  will  be  found  a  reference  to  the  water  and  wood  maids 

rail  .ire  of  a  beautiful  form  with  long  green  hair:     They 

swing  and  balance  themselves  on  the  branches  of  trees,  bathe  in  lakes  and 

v  on  the  surface  of  the  water,  and  wring  their  locks  on  the  green 

I  at  the  water's  edge."     On  fairies  and  carp  rings  see  Theodore  Gill  in 

.Smithsonian  Miscellaneous  Collections  48:203,  1905. 


Limnology 


knowledge  of  many  of  them  was  possible  so  long  as  the 
most  important  things  involved  in  them — often  even 
the  causative  organisms — could  not  be  seen.     Progress  , 
awaited  the  discovery  of  the  microscope. 

The  microscope  opened  a  new  world  of  life  to  human 
eyes— "the  world  of  the  infinitely  small  things."  It 
revealed  new  marvels  of  beauty  everywhere.     It  dis- 


Fig.  i.     Waterbloom   (Euglena)  on  the  surface  film  of  the  Renwick 
lagoon  at  Ithaca.     The  clear  streak  is  the  wake  of  a  boat  just  passed. 

covered  myriads  of  living  things  where  none  had  been 
suspected  to  exist,  and  it  brought  the  elements  of 
organic  structure  and  the  beginning  processes  of 
organic  development  first  within  the  range  of  our 
vision.  And  this  is  not  all.  Much  that  might  have 
been  seen  with  the  unaided  eye  was  overlooked  until 
the  use  of  the  microscope  taught  the  need  of  closer 
looking.  It  would  be  hard  to  overestimate  the  stimu- 
lating effect  of  the  invention  of  this  precious  instrument 
on  all  biological  sciences. 


16  Introduction 


With   such  crude  instruments  as  the  early  micro- 

ts  a  ailil  a  >mmand  they  began  to  explore  the  world 
.in.     They  looked  into  the  minute  structure  of 
■.•thing—  forms    of    crystals,    structure    of    tissues, 
s  of  insects,  hairs  and  fibers,  and,  above  all  else, 
micro-organisms  of  the  water.     These,  living  in  a 
rent  medium,  needed  only  to  be  lifted  in  a  drop 
i  >f  water  to  be  ready  for  observation.     At  once  the  early 
mieroscopists   became   most   ardent   explorers   of  the 
■   r.     They  found  every  ditch   and  stagnant  pool 
dng  with  forms,  new  and  wonderful  and  strange. 
ften  found  each  drop  of  water  inhabited.     They 
gained  a  new  conception  of  the  world's  fulness  of  life 
and  one  of  the  greatest  of  them  Roesel  von  Rosenhof, 
expressed  in  the  title  of  his  book,  "Insekten  Belusti- 
gung"*  the  pleasure  they  all  felt  in  their  work.      It  was 
the  joy  of  pioneering.     Little  wonder  that  during  a 
1«  >ng  period  of  exploration  microscopy  became  an  end 
in  it  self.     Who  that  has  used  a  microscope  has  not  been 
mated  on  first  acquaintance  with  the  dainty  ele- 
e  and  b<  tauty  of  the  desmids,  the  exquisite  sculptur- 
ing of  diatom  shells,  the  all-revealing  transparency  of 
the  daphnias,  etc.,  and  who  has  not  thereby  gained  a 
appreciation  of  the  ancient  saying,  Natura  maxime 
miranda  in  minimis.} 

Am<  >ng  these  pioneers  there  were  great  naturalists — - 
mmerdam  and  Leeuwenhoek  in  Holland,  the  latter, 
the  maker  of  his  own  lenses;  Malpighi  and  Redi  in 
I tcily;  Reaumer  and  Trembly  in  France;  the  above 
mentioned,  Roesel,  a  German,  who  was  a  painter  of 
miniatures;  and  many  others.  These  have  left  us 
faithful  records  of  what  they  saw,  in  descriptions  and 
res  that  in  many  biological  fields  are  of  more  than 
historical  importance.     These  laid  the  foundations  of 

:ng  =  delight. 
[Nature  is  most  wonderful  in  little  things. 


Important  Events  17 


our  knowledge  of  water  life.  Chiefly  as  a  result  of  their 
labor  there  emerged  out  of  this  ancient  "natural 
philosophy"  the  segregated  sciences  of  zoology  and 
botany.  Our  modern  conceptions  of  biology  came 
later,  being  based  on  knowledge  which  only  the  per- 
fected microscope  could  reveal.  — - — -    I — 

A  long  period  of  pioneer  exploration  resulted  in  the 
discovery  of  new  forms  of  aquatic  life  in  amazing 
richness  and  variety.  These  had  to  be  studied  and 
classified,  segregated  into  groups  and  monographed, 
and  this  great  survey  work  occupied  the  talents  of 
many  gifted  botanists  and  zoologists  through  two 
succeeding  centuries — indeed  it  is  not  yet  completed. 
But  about  two  centuries  after  the  construction  of  the 
first  microscope,  occurred  an  event  of  a  very  different 
kind,  that  was  destined  to  exert  a  profound  influence 
throughout  the  whole  range  of  biology.  This  was  the 
publication  of  Darwin's  Origin  of  Species.  This  book 
furnished  also  a  tool,  but  of  another  sort — a  tool  of  the 
mind.  It  set  forth  a  theory  of  evolution,  and  offered 
an  explanation  of  a  possible  method  by  which  evolution 
might  come  to  pass,  and  backed  the  explanation  with 
such  abundant  and  convincing  evidence  that  the 
theory  could  no  longer  be  ignored  or  scoffed  out  of 
court.  It  had  to  be  studied.  The  idea  of  evolution 
carried  with  it  a  new  conception  of  the  life  of  the  world. 
If  true  it  was  vastly  important.  Where  should  the 
evidence  for  proof  or  refutation  be  found?  Naturally, 
the  simpler  organisms,  of  possible  ancestral  character- 
istics, were  sought  out  and  studied,  and  these  live  in  the 
water.  Also  the  simpler  developmental  processes,  with 
all  they  offer  of  evidence;  and  these  are  found  in  the 
water.  Hence  the  study  of  water  life,  especially  with 
regard  to  structure  and  development,  received  a  mighty 
impetus  from  the  publication  of  this  epoch-making  book. 
The  half  century  that  has  since  elapsed  has  been  one  of 
unparalleled  activity  in  these  fields. 


1 8  Introduction 


Almost  simultaneously  with  the  appearance  of 
win's  great  work,  there  occurred  another  event 
which  did  more  perhaps  than  any  other  single  thing  to 
bring  about  the  recognition  of  the  limnological  part  of 
the  field  of  biology  as  one  worthy  of  a  separate  recogni- 
ti(  -n  and  a  name.  This  was  the  discovery  of  plancton 
—that  free-floating  assemblage  of  organisms  in  great 
water  masses,  that  is  self-sustaining  and  self -maintaining 
and  that  is  independent  of  the  life  of  the  land.  Lilje- 
borg  and  Sars  found  it,  by  drawing  fine  nets  through 
tin-  waters  of  the  Baltic.  They  found  a  whole  fauna 
and  flora,  mostly  microscopic — a  well  adjusted  society 
of  organisms,  with  its  producing  class  of  synthetic 
plant  forms  and  its  consuming  class  of  animals;  and 
among  the  animals,  all  the  usual  social  groups,  herbi- 
v  >res  and  carnivores,  parasites  and  scavengers.  Later, 
this  assemblage  of  minute  free-swimming  organisms 
was  named  plancton.*  After  its  discovery  the  seas 
could  no  longer  be  regarded  as  "barren  wastes  of 
waters";  for  they  had  been  found  teeming  with  life. 
This  discovery  initiated  a  new  line  of  biological  explora- 
tion, the  survey  of  the  life  of  the  seas.  It  was  simple 
matter  to  draw  a  fine  silk  net  through  the  open  water 
and  c<  tllect  everything  contained  therein.  There  are 
no  obstructions  or  hiding  places,  as  there  are  every- 
where on  land;  and  the  fine  opportunity  for  quantita- 
tive as  well  as  qualitative  determination  of  the  life  of 
water  areas  was  quickly  grasped.  The  many  expedi- 
tions that  have  been  sent  out  on  the  seas  and  lakes  of 
the  world  have  resulted  in  our  having  more  accurate 
and  detailed  knowledge  of  the  total  life  of  certain  of 
these  waters  than  we  have,  or  are  likely  to  be  able  soon 
to  acquire,  of  life  on  land. 

Pr<  aninent  among  the  investigators  of  fresh  water  life 
in  America  during  the  nineteenth  century  were  Louis 

*Planktos  =  driftin  \  free  floating. 


Aquatic  Life  19 


Agassiz,  an  inspiring  teacher,  and  founder  of  the  first 
of  our  biological  field  stations;  Dr.  Joseph  Leidy,  an 
excellent  zoologist  of  Philadelphia,  and  Alfred  C.  Stokes 
of  New  Jersey,  whose  Aquatic  Microscopy  is  still  a  use- 
ful handbook  for  beginners. 

Our  knowledge  of  aquatic  life  has  been  long  accumu- 
lating. Those  who  have  contributed  have  been  of  very 
diverse  training  and  equipment  and  have  employed 
very  different  methods.  Fishermen  and  whalers;  col- 
lectors and  naturalists;  zoologists  and  botanists,  with 
specialists  in  many  groups;  water  analysts  and  sani- 
tarians; navigators  and  surveyors;  planktologists  and 
bacteriologists,  and  biologists  of  many  names  and  sorts 
and  degrees ;  all  have  had  a  share.  For  the  water  has 
held  something  of  interest  for  everyone. 

Fishing  is  one  of  the  most  ancient  of  human  occupa- 
tions; and  doubtless  the  beginning  of  this  science  was 
made  by  simple  fisher-folk.  Not  all  fishing  is,  or  ever 
has  been,  the  catching  of  fish.  The  observant  fisherman 
has  ever  wished  to  know  more  of  the  ways  of  nature,  and 
science  takes  its  origin  in  the  fulfillment  of  this  desire. 

The  largest  and  the  smallest  of  organisms  live  in  the 
waterTand  no  one  was  ever  equipped,  or  will  ever  be 
equipped  to  study  any  considerable  part  of  them. 
Practical  difficulties  stand  in  the  way.  One  may  not 
catch  whales  and  water-fleas  with  the  same  tackle,  nor 
weigh  them  upon  the  same  balance.  Consider  the  dif- 
ference in  equipment,  methods,  area  covered  and  num- 
bers caught  in  a  few  typical  kinds  of  aquatic  collecting : 

(1).  Whaling  involves  the  cooperative  efforts  of 
many  men  possessed  of  a  specially  equipped  vessel.  A 
single  specimen  is  a  good  catch  and  leagues  of  ocean 
may  have  to  be  traversed  in  making  it. 

(2).  Fishing  may  be  done  by  one  person  alone, 
equipped  with  a  hook  and  line.  An  acre  of  water  affords 
area  enough  and  ten  fishes  may  be  called  a  good  catch. 


i 


20 


Introduction 


l  .  G  Meeting  the  commoner  invertebrates,  such  as 
water  insects,  crustaceans  and  snails  involves  ordinarily 
the  use  of  a  hand  net.  A  square  rod  of  water  is  suffi- 
cient area  to  ply  it  in;  a  satisfactory  catch  may  be  a 
hundred  specimens. 

(4).  For  collecting  entomostracans  and  the  larger 
planet*  >n  1  >rganisms  t<  >wing  nets  of  fine  silk  bolting-cloth 
are  cxHnmonly  employed.  Possibly  a  cubic  meter  of 
r  is  strained  and  a  good  catch  of  a  thousand  speci- 
mens may  result. 

(5).  The  microplancton  organisms  that  slip  through 
the  meshes  of  the  finest  nets  are  collected  by  means  of 
a  nt  ri  fuge  and  filter.  A  liter  of  water  is  often  an  ample 
field  for  finding  ten  thousand  specimens. 

(6).  Last  and  least  are  the  water  bacteria,  which  are 
gathered  by  means  of  cultures.  A  single  drop  of  water 
will  often  furnish  a  good  seeding  for  a  culture  plate 
yielding  hundreds  of  thousands  of  specimens. 

Thus  the  field  of  operation  varies  from  a  wide  sea  to 
a  single  drop  of  water  and  the  weapons  of  chase  from 
a  harpoon  gun  to  a  sterilized  needle.  Such  divergencies 
have  from  the  beginning  enforced  specialization  among 
limnological  workers,  and  different  methods  of  studying 
the  problems  of  water  life  have  grown  up  wide  apart, 
and,  often,  unfortunately,  without  mutual  recognition. 
The  educational,  the  economic  and  the  sanitary  inter- 
ests of  the  people  in  the  water  have  been  too  often  dealt 
with  as  though  they  are  wholly  unrelated. 

The  agencies  that  in  America  furnish  aid  and  support 
t<  >  investigations  in  fresh  water  biology  are  in  the  main: 

1.  Universities  which  give  courses  of  instruction 
in  limnology  and  other  biological  subjects,  and  some  of 
which  maintain  field  stations  or  laboratories  for  investi- 
gation of  water  problems.  2.  National,  state  and 
municipal  boards  and  surveys,  which  more  or  less 
constantly  maintain  researches  that  bear  directly  upon 


Investigations  21 


their  own  economic  or  sanitary  problems.  3.  Socie- 
ties, academies,  institutes,  museums,  etc.,  which 
variously  provide  laboratory  facilities  or  equip  expedi- 
tions or  publish  the  results  of  investigations.  4. 
Private  individuals,  who  see  the  need  of  some  special 
investigation  and  devote  their  means  to  furthering  it. 
The  Universities  and  private  benefactors  do  most  to 
care  for  the  researches  in  fundamental  science.  Fish 
commissions  and  sanitary  commissions  support  the 
applied  science.  Governmental  and  incorporated  insti- 
tutions assist  in  various  ways  and  divide  the  main  work 
of  publishing  the  results  of  investigations. 

It  is  pioneer  limnological  work  that  these  various 
agencies  are  doing;  as  yet  it  is  all  new  and  uncorre- 
cted. It  is  all  done  at  the  instance  of  some  newly 
discovered  and  pressing  need.  America  has  quickly 
passed  from  being  a  wilderness  into  a  state  of  highly 
artificial  culture.  In  its  centers  of  population  great 
changes  of  circumstances  have  come  about  and  new 
needs  have  suddenly  arisen.  First  was  felt  the  failure 
of  the  food  supply  which  natural  waters  furnished; 
and  this  lack  led  to  the  beginning  of  those  limnological 
enterprises  that  are  related  to  scientific  fish  culture. 
Next  the  supply  of  pure  water  for  drinking  failed  in  our 
great  cities;  knowledge  of  water-borne  diseases  came 
to  the  fore:  knowledge  of  the  agency  of  certain 
aquatic  insects  as  carriers  of  dread  diseases  came  in; 
and  suddenly  there  began  all  those  limnological  enter- 
prises that  are  connected  with  sanitation.  Lastly,  the 
failure  of  clean  pleasure  grounds  by  the  water-side, 
and  of  wholesome  places  of  recreation  for  the  whole 
people  through  the  wastefulness  of  our  past  methods  of 
exploitation,  through  stream  and  lake  despoiling,  has 
led  to  those  broader  limnological  studies  that  have  to 
do  with  the  conservation  of  our  natural  resources. 


Biological  Field  Stations  23 


~  o 


WASH'S   .it  jjg^    b   id^    o\s   -ha    ^ 
*0|  23i|^<3|l  gs  -all  $31*3*5,8  g-J 

»  uf.i  i: tUuffl &<tx&£  *i 

§  fJSjili^SJffilfjflilfj!  jilll 

£  ^        >  ^        ^  j     co     O        Q        O     .  §        O 

s  I II .IIP  lilj  PlJl  ill  iiiiii 

E  1 1ff  *tf  *S^  d;-s«L|  aius|su€|5 

§  s  |ir|;l  i!il|i|teil  ^nfitini 
S  I  f ll  8113  fr  BWa^U  ill  II  ll  II J  ^ 

2SQW  fe  S  Q  E      £      £      £ 

CO    '*-• 

^      C      M  n  o  ^  in  ^d        »C      od        cf* 


* 


§  H  I  llsi-s  e|  *^  fisll  ra|  «3. 


u  o 


S     iis^nih  sis  °8a-a    sia  ill  ?s 


o-° 


Sum;  ri  jifiii"iii  in-8  „  a^M  § 


72 


Ah  co    a        O  m        W        £ 


ATEK 


ALL  inorganic  substances, 
acting  in  their  own  proper 
nature,  and  without  assist- 
ance or  combination,  water 
is  the  most  wonderful.  If 
we  think  of  it  as  the  source 
of  all  the  changefidness  and 
beauty  which  we  have  seen 
in  the  clouds;  then  as  the  instrument  by  which  the  earth  we  have 
contemplated  was  modelled  into  symmetry,  and  its  crags  chiseled  into 
grace;  then  as,  in  the  form  of  snow,  it  robes  the  mountains  it  has 
made,  with  that  transcendent  light  which  we  could  not  have  conceived 
if  we  had  not  seen ;  then  as  it  exists  in  the  foam  of  the  torrent,  in  the 
iris  which  spans  it,  in  the  morning  mist  which  rises  from  it,  in  the 
deep  crystalline  pools  which  mirror  its  hanging  shore,  in  the  broad 
lake  and  glancing  river,  finally,  in  that  which  is  to  all  human  minds 
the  best  emblem  of  unwearied,  unconquerable  power,  the  wild,  various, 
fantastic,  tameless  unity  of  the  sea;  what  shall  we  compare  to  this 
mighty,  this  universal  clement,  for  glory  and  for  beauty?  or  how  shall 
we  follow  its  eternal  cheerfulness  of  feeling?  It  is  like  trying  to  paint 
a  soul."  -  RuSKIN. 


24 


CHAPTER  II 


THE  NATURE  OF  AQUATIC 
ENVIRONMENT 


PROPERTIES 

AND   USES 

ATER,  the  one  abundant 
liquid  on  earth,  is,  when 
pure,  tasteless,  odorless 
and  transparent.  Wa- 
ter is  a  solvent  of  a 
great  variety  of  sub- 
stances, both  solid  and 
gaseous.  Not  only  does 
it  dissolve  more  sub- 
stances than  any  other 
liquid,  but,  what  is  more 
important,  it  dissolves 
those  substances  which 
are  most  needed  in  solution  for  the  maintenance  of 
life.  Water  is  the  greatest  medium  of  exchange  in  the 
world.  It  brings  down  the  gases  from  the  atmosphere; 
it  transfers  ammonia  from  the  air  into  the  soil  for 
plant  food;  it  leaches  out  the  soluble  constituents 
of  the  soil;  and  it  acts  of  itself  as  a  chemical  agent 
in  nutrition,  and  also  in  those  changes  of  putrefaction 
and  decay  that  keep  the  world's  available  food  supply 
in  circulation. 

^  Water  is  nature's    great    agency    for   the  applica- 
tion of  mechanical  energy.     It  is  by  means  of  water 

25 


26  Nature  of  Aquatic  Environment 

that  deltas  are  built  and  hills  eroded.     Water  is  the 
chief  factor  in  all  those  eternal  operations  of  flood  and 
by  which  the  surface  of  the  continent  is  shaped. 

Transparency— Water  has  many  properties  that  fit 
it  for  being  the  abode  of  organic  life.  Second  only  in 
importance  to  its  power  of  carrying  dissolved  food 
materials  is  its  transparency.  It  admits  the  light  of 
the  sun;  and  the  primary  source  of  energy  for  all 
organic  life  is  the  radiant  energy  of  the  sun.  Green 
1  .lants  use  this  energy  directly;  animals  get  it  in- 
directly with  their  food.  Green  plants  constitute 
the  producing  class  of  organisms  in  water  as  on  land. 
Just  in  proportion  as  the  sun's  rays  are  excluded, 
the  process  of  plant  assimilation  (photosynthesis)  is 
impeded.  When  we  wish  to  prevent  the  growth  of 
algae  or  other  green  plants  in  a  reservoir  or  in  a  spring 
we  cover  it  to  exclude  the  light.  Thus  we  shut  off 
the  power. 

Pure  water,  although  transparent,  absorbs  some  of 
the  energy  of  the  sun's  rays  passed  through  it,  and 
water  containing  dissolved  and  suspended  _  matter 
(such  as  are  present  in  all  natural  water)  impedes 
their  passage  far  more.  From  wThich  it  follows,  that 
the  superficial  layer  of  a  body  of  water  receives  the 
most  light.  Penetration  into  the  deeper  strata  is 
impeded  according  to  the  nature  of  the  water  content. 
Dissolved  matters  tint  the  water  more  or  less  and  give 
it  color.  Every  one  knows  that  bog  waters,  for 
example,  are  dark.  They  look  like  tea,  even  like  very 
strong  tea,  and  like  tea  they  owe  their  color  to  their 
content  of  dissolved  plant  substances,  steeped  out  of 
the  peaty  plant  remains  of  the  bog. 

Suspended  matters  in  the  water  cause  it  to  be  turbid. 
These  may  be  either  silt  and  refuse,  washed  in  from 
the  land,  or  minute  organisms  that  have  grown  up  in 


Transparency  27 


the  water  and  constitute  its  normal  population.  One 
who  has  carefully  watched  almost  any  of  our  small 
northern  lakes  through  the  year  will  have  seen  that 
its  waters  are  clearest  in  February  and  March,  when 
there  is  less  organic  life  suspended  in  them  than  at 
other  seasons.  But  it  is  the  suspended  inorganic 
matter  that  causes  the  most  marked  and  sudden 
changes  in  turbidity — the  washings  of  clay  and  silt 
from  the  hills  into  a  stream;  the  stirring  up  of  mud 
from  the  bottom  of  a  shallow  lake  with  high  winds. 
The  difference  in  clearness  of  a  creek  at  flood  and  at 
low  water,  or  of  a  pond  before  and  after  a  storm  is  often 
very  striking. 

Such  sudden  changes  of  turbidity  occur  only  in  the 
lesser  bodies  of  water;  there  is  not  enough  silt  in  the 
world  to  make  the  oceans  turbic. 

The  clearness  of  the  water  determines  the  depth 
at  which  green  plants  can  flourish  in  it.  Hence  it  is 
of  great  importance,  and  a  number  of  methods  have 
been  devised  for  measuring  both  color  and  turbidity. 
A  simple  method  that  was  first  used  for  comparing  the 
clearness  of  the  water  at  different  times  and  places 
and  one  that  is,  for  many  purposes,  adequate,  and  one 
that  is  still  used  more  widely  than  any  other,*  consists 
in  the  lowering  of  a  white  disc  into  the  water  and  record- 
ing the  depth  at  which  it  disappears  from  view.  The 
standard  disc  is  20  cm.  in  diameterf;  it  is  lowered 
in  a  horizontal  position  during  midday  light.  The 
depth  at  which  it  entirely  disappears  from  view  is 
noted.  It  is  then  slowly  raised  again  and  the  depth 
at  which  it  reappears  is  noted.  The  mean  of  these 
two  measurements  is  taken  as  the  depth  of  its  visibility 


*Method  of  Secchi:  for  other  methods,  see  Whipple's  Microscopy  of  Drink- 
ing Water,  Chap.  V.     Steuer's  Planktonkunde,  Chapter  III. 

fWhipple  varied  it  with  black  quadrants,  like  a  surveyor's  level-rod  target 
and  viewed  it  through  a  water  telescope. 


28  ture  of  Aquatic  Environment 

beneath  the  Such  a  disc  has  been  found  to 

disappear  at  very  different  depths.  Witness  the  fol- 
lowing typical  examples: 

Pa  :       '                 59  meters 

Med               in  Sea    42  meters 

33  meters 

a    21  meters 

5  meters 

■   ark),  Mar  o  meters 

i     -Kirk).  Aug 5  meters 

Fure  Lake  (Denmark).  Dec 7  meters 

•■  m  River  (111.)  under  ice : 3.65  meters 

River  I  111.)  at  flood 013  meters 

It  is  certain  that  diffused  light  penetrates  beyond  the 
depth  at  which  Secchi's  disc  disappears.  In  Lake 
Geneva,  for  example,  where  the  limit  of  visibility  is 
21m.  photographic  paper  sensitized  with  silver  chloride 
ceased  to  be  affected  by  a  24-hour  exposure  at  a  depth 
of  about  1 00  meters  or  when  sensitized  with  iodobromide 
of  silver,  at  a  depth  about  twice  as  great.  Below  this 
depth  the  darkness  appears  to  be  absolute.  Indeed  it 
is  deep  darkness  for  the  greater  part  of  this  depth,  90 
meters  being  set  down  as  the  limit  of  ''diffused  light." 
How  far  down  the  light  is  sufficient  to  be  effective  in 
photosynthesis  is  not  known,  but  studies  of  the  distri- 
bution in  depth  of  fresh  water  algae  have  shown  them 
to  be  chiefly  confined,  even  in  clear  lakes,  to  the  upper- 
most 20  meters  of  the  water.  Ward  ('95)  found  64 
per  cent,  of  the  plancton  of  Lake  Michigan  in  the  upper- 
most two  meters  of  water,  and  Reighard  ('94)  found 
similar  conditions  in  Lake  St.  Clair.  Since  the  inten- 
sity of  the  light  decreases  rapidly  with  the  increase  in 
depth  it  is  evident  that  only  those  plants  near  the  sur- 
face of  the  water  receive  an  amount  of  light  comparable 
with  that  which  exposed  land  plants  receive.  Less  than 
this  seems  to  be  needed  by  most  free  swimming  algae, 


Transparency 


29 


since  they  are  often  found  in  greatest  number  in  open 
waters  some  five  to  fifteen  meters  below  the  surface. 
Some  algae  are  found  at  all  depths,  even  in  total  dark- 
ness on  the  bottom;  notably  diatoms,  whose  heavy 
silicious  shells  cause  them  to  sink  in  times  of  prolonged 
calm,  but  these  are  probably  inactive  or  dying  individ- 
uals. There  are  some  animals,  however,  normally 
dwelling  in  the  depths  of  the  water,  living  there  upon 


l&OiMeters  DeptA 
Fig.  3.  _  Diagram  illustrating  the  penetration  of  light  into  the  water  of  a  lake; 
also,  its  occlusion  by  inflowing  silt  and  by  growths  of  plants  on  the  surface. 

the  organic  products  produced  in  the  zone  of  photo- 
synthesis above  and  bestowed  upon  them  in  a  consider- 
able measure  by  gravity.  To  the  consideration  of 
these  we  will  return  in  a  later  chapter. 

The  accompanying  diagram  graphically  illustrates 
the  light  relations  in  a  lake.  The  deeper  it  is  the  greater 
its  mass  of  unlighted  and,  therefore,  unproductive 
water,  and  the  larger  it  be,  the  less  likely  is  its  upper 
stratum  to  be  invaded  by  obscuring  silt  and  water 
weeds. 


30  X (it urc  of  Aquatic  Environment 

Mobility — Water  is  the  most  mobile  of  substances, 
yet  it  is  not  without  internal  friction.  Like  molasses, 
it  stiffens  with  cooling  to  a  degree  that  affects  the 
flotation  of  micro-organisms  and  of  particles  suspended 
in  it.  Its  viscosity  is  twice  as  great  at  the  freezing 
point  as  at  ordinary  summer  temperature  (77°F.). 

Buoyancy  -Water  is  a  denser  medium  than  air;  it 
775  time's  heavier.  Hence  the  buoyancy  with  which 
it  supports  a  body  immersed  in  it  is  correspondingly 
greater.  The  density  of  water  is  so  nearly  equal  to 
that  of  protoplasm,  that  all  living  bodies  will  float  in 
it  with  the  aid  of  very  gentle  currents  or  of  a  very  little 
exertion  in  swimming.  Flying  is  a  feat  that  only  a 
few  of  the  most  specialized  groups  of  animals  have 
mastered,  but  swimming  is  common  to  all  the  groups. 

Pressure — This  greater  density,  however,  involves 
greater  pressure.  The  pressure  is  directly  proportional 
to  the  depth,  and  is  equal  to  the  weight  of  the  super- 
posed column  of  water.  Hence,  wTith  increasing  depth 
the  pressure  soon  becomes  enormous,  and  wholly  insup- 
portable by  bodies  such  as  our  own.  Sponge  fishers 
and  pearl  divers,  thoroughly  accustomed  to  diving, 
descending  naked  from  a  boat  are  able  to  work  at  depths 
up  to  20  meters.  Professional  divers,  encased  in  a 
modern  diving  dress  are  able  to  work  at  depths  several 
times  as  great;  but  such  depths,  when  compared  with 
the  depths  of  the  great  lakes  and  the  oceans  are  com- 
parative shoals. 

Beyond  these  depths,  however,  even  in  the  bottom 
of  the  seas,  animals  live,  adjusted  to  the  great  pressure, 
which  may  be  that  of  several  hundred  of  atmospheres. 
But  these  cannot  endure  the  lower  pressure  of  the 
surface,  and  when  brought  suddenly  to  the  surface  they 
burst.  Fishes  brought  up  from  the  bottom  of  the 
deeper   freshwater   lakes,    reach    the    surface    greatly 


Maximum  Density 


31 


swollen,  their  scales  standing  out  from  the  body,  their 
eyes  bulging. 

Maximum  density — Water  contracts  on  cooling,  as  do 
other  substances,  but  not  to  the  freezing  point — only 
to  40  centigrade  (39. 2°  Fahrenheit).  On  this  pecu- 
liarity hang  many  important  biological  consequences. 
Below  40  C.  it  begins  to  expand  again,  becoming  lighter, 
as  shown  in  the  accompanying  table: 


Temp* 

mature 

Weight  in  lbs. 

C° 

F° 

percu.  ft. 

Density 

35 

95 

62,060 

.99418 

21 

7c 

62.303 

.99802 

10 

50 

62.40S 

■99975 

4 

39 

62.425 

1. 00000 

0 

32 

62.417 

.99987 

Hence,  on  the  approach  of  freezing,  the  colder  lighter 
water  accumulates  at  the  surface,  and  the  water  at  the 
point  of  maximum  density  settles  to  the  bottom,  and 
the  congealing  process,  so  fatal  to  living  tissues  generally 
is  resticted  to  a  thin  top  layer.  Here  at  o°  C.  (320  F.) 
the  water  freezes,  expanding  about  one-twelfth  in  bulk 
in  the  resulting  ice  and  reducing  its  weight  per  cubic 
foot  to  57.5  pounds. 

Stratification  of  the  water — Water  is  a  poor  conductor 
of  heat.  We  recognize  this  when  we  apply  heat  to  the 
bottom  of  a  vessel,  and  set  up  currents  for  its  distribution 
through  the  vessel.  We  depend  on  convection  and  not 
on  conduction.  But  natural  bodies  of  water  are  heated 
and  cooled  from  the  top,  when  they  are  in  contact  with 
the  atmosphere  and  where  the  sun's  rays  strike. 
Hence,  it  is  only  those  changes  of  temperature  which 
increase  the  density  of  the  surface  waters  that  can  pro- 
duce convection  currents,  causing  them  to  descend,  and 
deeper  waters  to  rise  in  their  place.  Minor  changes 
of  this  character,  verv  noticeable  in  shallow  water,  occur 


32 


Nature  of  Agnatic  Environment 


every  clear  day  with  the  going  down  of  the  sun,  but 
great  changes,  imp  irtant  enough  to  affect  the  tempera- 
ture of  all  the  waters  of  a  deep  lake,  occur  but  twice  a 
.  and  they  follow  the  precession  of  the  equinoxes. 
Tlure  is  a  brief,  often  interrupted,  period  (in  March 
in  the  latitude  of  Ithaca)  after  the  ice  has  gone  out,  while 
the  surface  waters  are  being  warmed  to  o°C;  and 
there  is  a  1<  aiger  peri<  >d  in  autumn,  while  they  are  being 
led  to  0°C.     Between  times,  the  deeper  waters  of 


WINTER 


SUMMER 


4 
PlG.  4 


Diagram  illustrating  summer  and  winter  temperature  conditions  in 
Cayuga  Lake.     The  spacing  of  the  horizontal  lines  represents 
equal  temperature  intervals. 


a  lake   are  at  rest,  and  they  are   regularly  stratified 
according  to  their  density. 

In  deep  freshwater  lakes  the  bottom  temperature 
remains  through  the  year  constantly  near  the  point  of 
maximum  density,  40  C.  This  is  due  to  gravity.  The 
heavier  water  settles,  the  lighter,  rises  to  the  top. 
Were  gravity  alone  involved  the  gradations  of  tempera- 
ture from  bottom  to  top  would  doubtless  be  perfectly 
regular  and  uniform  at  like  depths  from  shore  to  shore. 
But  springs  of  ground  water  and  currents  come  in  to 


Lake   Temperatures 


33 


disturb  the  horizontal  uniformity,  and  winds  may  do 
much  to  disturb  the  regularity  of  gradations  toward  the 
surface.  Water  temperatures  are  primarily  dependent 
on  those  of  the  superincumbent  air.  The  accompany- 
ing diagram  of  comparative  yearly  air  and  water 
temperatures  in  Hallstatter  Lake  (Austria)  shows 
graphically  the  diminishing  influence  of  the  former  on 
the  latter  with  increasing  depth. 


i 


JO 


JO 


60 


loo 


fun 


-3 


§> 
^ 


£ 


o\      I      I      1      1  j  . 

vf- - 

0- 


Fig.  5.     Diagram  illustrating  the  relation  of  air  and  water  temperatures  at 
varying  depths  of  water  in  Hallstatter  Lake  (after  Lorenz). 


Nature  of  Aquatic  Environment 


FlG.  6.     Diagram  illustrating  the  distribution  of  temperature  in  Cayuga  Lake 

throughout  the  year.     (Extremes:     not  normal). 

The  yearly  cycle — The  general  relation  between  sur- 
face  and  bottom  temperatures  for  the  year  are  graphi- 
cally shown  in  the  accompanying  diagram,  wherein  the 
tw<  >  peri<  dsof  thermal  stratification,  "direct"  in  summer 
when  the  warmer  waters  are  uppermost,  and  "inverse" 
in  winter  when  the  colder  waters  are  uppermost,  are 
separated  by  two  periods  of  complete  circulation,  when 
all  tlie  waters  of  the  lake  are  mixed  at  40  C.  The  range 
of  temperatures  from  top  to  bottom  is  much  greater  in 
the  summer  "stagnation  period";    nevertheless  there 


The  Yearly  Cycle  35 


is  more  real  stagnation  during  the  winter  period;  for, 
after  the  formation  of  a  protecting  layer  of  ice,  this 
shuts  out  the  disturbing  influence  of  wind  and  sun  and 
all  the  waters  are  at  rest.  The  surface  temperature 
bears  no  further  relation  to  air  temperature  but  remains 
constantly  at  o°  C. 

After  the  melting  of  the  ice  in  late  winter  the  surface 
waters  begin  to  grow  warmer;  so,  they  grow  heavier, 
and  tend  to  mingle  with  the  underlying  waters.  When 
all  the  water  in  the  lake  is  approaching  maximum 
density  strong  winds  heaping  the  waters  upon  a  lee 
shore,  may  put  the  entire  body  of  the  lake  into  complete 
circulation.  How  long  this  circulation  lasts  will  depend 
on  the  weather.  It  will  continue  (with  fluctuating 
vigor)  until  the  waters  are  warm  enough  so  that  their 
thermal  stratification  and  consequent  resistance  to 
mixture  are  great  enough  to  overcome  the  disturbing 
influence  of  the  wind.  Thereafter,  the  surface  may  be 
stirred  by  storms  at  any  time,  but  the  deeper  waters  of 
the  lake  will  have  passed  into  their  summer  rest. 

On  the  approach  of  autumn  the  cooling  of  surface 
waters  starts  convection  currents,  which  mix  at  first  the 
upper  waters  only,  but  which  stir  ever  more  deeply  as 
the  temperature  descends.  When  nearly  4°C,  with 
the  aid  of  winds,  the  entire  mass  of  water  is  again  put 
in  circulation.  The  temperature  is  made  uniform 
throughout,  and  what  is  more  important  biologically, 
the  contents  of  the  lake,  in  both  dissolved  and  suspended 
matters,  are  thoroughly  mixed.  Nothing  is  thereafter 
needed  other  than  a  little  further  cooling  of  the  surface 
waters  to  bring  about  the  inverse  stratification  of  the 
winter  period. 

Vernal  and  autumnal  circulation  periods  differ  in 
this,  that  convection  currents  have  a  smaller  share,  and 
winds  may  have  a  larger  share  in  the  former.  For  the 
surface  waters  are  quickly  warmed  from  o°  C.  to  40  C.f 


36  Nature  of  Aquatic  Environment 


and  further  warming  induces  no  descending  currents, 
but  instead  tends  toward  greater  stability.  It  some- 
times happens  that  in  shallow  lakes  there  is  little  vernal 
circulation.     If  the  water  be  warmed  at  40  C.  at  the 

1  ottom  before  the  ice  is  entirely  gone,  and  if  a  period 
of  calm  immediately  follow,  so  that  no  mixing  is  done 
by  the  wind,  there  may  be  no  general  spring  circulation 
whatever. 

The  shallower  the  lake,  other  things  being  equal,  the 
greater  will  be  the  departure  of  temperature  conditions 
from  those  just  sketched,  for  the  greater  will  be  the 
disturbing  influence  of  the  wind.  In  south  temperate 
lakes,  temperature  conditions  are,  of  course,  reversed 
with  the  seasons.  In  tropical  lakes  whose  surface 
temperature  remains  always  above  40  C,  there  can  be 
no  complete  circulation  from  thermal  causes,  and  in- 
verse stratification  is  impossible.  In  polar  lakes,  never 
freed  fr<»m  ice,  no  direct  stratification  is  possible. 

It  follows  from  the  foregoing  that  gravity  alone  may 
do  something  toward  the  warming  of  the  waters  in  the 
spring,  and  much  toward  the  cooling  of  them  in  the  fall. 
gravity  they  will  be  made  to  circulate  until  they 
reach  the  point  of  maximum  density,  when  going  either 
up  ( >r  d<  >wn  the  scale.  Beyond  this  point,  howrever, 
gravity  tends  to  stabilize  them.  The  wrind  is  responsi- 
}  le  f<  -r  the  further  warming  of  the  waters  in  early  sum- 
mer, and  the  heat  in  excess  of  40  C.  has  been  called  by 
Birge  and  Juday  "wind-distributed"  heat.  They  esti- 
•  that  it  may  amount  to  30,000  gram-calories  per 
square  centimeter  of  surface  in  such  lakes  as  those 
of  Central  New  York,  and  the  following  figures  for 
Cayuga  Lake  show  its  distribution  by  depth  in  August, 
I'M  1,  in  percentage  remaining  at  successive  ten-meter 
intervals  In-low  the  surface: 


Below 

0 

1 0 

20 

30 

40 

50 

60 

70 

So   100 

133   meter? 

100 

- 

>"•: 

7-r 

3-7 

2.4 

1.8 

1 .2 

•7      3 

remaining 

Thermocline  37 


These  figures  indicate  the  resistance  to  mixing  that 
gravity  imposes,  and  show  that  the  wind  is  not  able  to 
overcome  it  below  rather  slight  depths. 

Vernal  and  autumnal  periods  of  circulation  ha</e  a 
very  great  influence  upon  the  distribution  of  both 
organisms  and  their  food  materials  in  a  lake;  to  the 
consideration  of  this  we  will  have  occasion  to  return 
later. 

The  thermocline — In  the  study  of  lake  temperatures 
at  all  depths,  a  curious  and  interesting  peculiarity  of 
temperature  interval  has  been  commonly  found  per- 
taining to  the  period  of  direct  stratification  (mid- 
summer). The  descent  in  temperature  is  not  regular 
from  surface  to  bottom,  but  undergoes  a  sudden  acceler- 
ation during  a  space  of  a  very  few  meters  some  distance 
below  the  surface.  The  stratum  of  water  in  which 
this  sudden  drop  of  temperature  occurs  is  known  as  the 
thermocline  (German,  Sprungschicht).  It  appears  to 
represent  the  lower  limit  of  the  intermittent  summer 
circulation  due  to  winds.  Above  it  the  waters  are  more 
or  less  constantly  stirred,  below  it  they  lie  still.  This 
interval  is  indicated  by  the  shading  on  the  right  side  of 
figure  4.  Birge  has  designated  the  area  above  the 
thermocline  as  the  epilimnion;  the  one  below  it  as 
hypolimnion. 

Further  study  of  the  thermocline  has  shown  that  it  is 
not  constant  in  position.  It  rises  nearer  to  the  surface 
at  the  height  of  the  midsummer  season  and  descends  a 
few  meters  with  the  progress  of  the  cooling  of  the 
autumnal  atmosphere.  This  may  be  seen  in  figure  7, 
which  is  Birge  and  Juday's  chart  of  temperatures  of 
Lake  Mendota  as  followed  by  them  through  the  season 
of  direct  stratification  and  into  the  autumnal  circula- 
tion period  in  1906.  This  chart  shows  most  graphically 
the  growing  divergence  of  surface  and  bottom  tempera- 
tures up  to  August,  and  their  later  approximation  and 


38 


Nature  of  Aquatic  Environment 


final  coalescence  in  October.  Leaving  aside  the  not 
unusual  erratic  features  of  surface  temperature  (repre- 
sented by  the  topmost  contour  line)  it  will  be  noticed 
that  thnv  is  a  wider  interval  somewhere  between  8  and 
16  meters  than  any  other  interval  either  above  or  below 
it.  S<  mutinies  it  falls  across  two  spaces  and  is  rendered 
apparent  in  the  charting  by  the  selection  of  inter- 
vals. It  first  appears  clearly  in  June  at  the  10-12  meter 
interval.     It  rises  in  July  above  the   10  meter  level. 


MAT                                                             JUNC 

JULT                                           AUG.                                          Sr-                                           OCT 

^^/vC_^^\i     0         i              j 

J« 

.    Fy/^     1A,  i       i 

n 

~7\\\/  /    \  ^mi         i 

M 

fL  \Jr    /         \  /  Y\  ^^^Hn 

11 

it 

/      -sj     n  2%</     /*    1  ,                         ,5^>-  /    W-^ 

14 

\*/          ^-"i      ^>—~^-—~^  1  '^^^jE/r-*^    ' 

1/  /   \/   '                                                           1                              '                -   -          i                             1 

r 

:                 i                  i                 1 

Fig.  7.  Temperature  of  the  water  at  different  depths  in  Lake  Mendota  in 
1906.  The  vertical  spaces  represent  degrees  Centigrade  and  the  figures 
attached  to  the  curves  indicate  the  depths  in  meters.     (Birge  and  Juday). 

In  the  middle  of  August  it  lies  above  the  8  meter  level, 
though  it  begins  to  descend  later  in  the  month.  It 
continues  to  descend  through  September,  and  is  found 
in  early  October  between  16  and  18  meters.  It  dis- 
a]  >]  ►ears  with  the  beginning  of  the  autumnal  circulation. 
The  cause  of  this  phenomenon  is  not  known.  Richter 
has  suggested  that  convection  currents  caused  by  the 
nocturnal  cooling  of  the  surface  water  after  hot  summer 
days  may  be  the  cause  of  it.     If  the  surface  waters  were 


Circulation  39 


cooled  some  degrees  they  would  descend,  displacing  the 
layers  underneath  and  setting  up  shallow  currents 
which  would  tend  to  equalize  the  temperature  of  all  the 
strata  involved  therein.  And  if  the  gradation  of  tem- 
peratures downward  were  regular  before  this  mixing, 
the  result  of  it  would  be  a  sudden  descent  at  its  lower 
limit,  after  the  mixing  was  done.  This  would  account 
for  the  upper  boundary  of  the  thermocline,  but  not  for 
its  lower  one.  Perhaps  an  occasional  deeper  mixing, 
extending  to  its  lower  boundary,  and  due  possibly  to 
high  winds,  might  bring  together  successional  lower 
levels  of  temperature  of  considerable  intervals.  Perhaps 
the  thermocline  is  but  an  accumulation  of  such  sort  of 
thermal  disturbance-records,  ranged  across  the  vertical 
section  of  the  lake,  somewhat  as  wave-drift  is  ranged  in 
a  shifting  zone  along  the  middle  of  a  sloping  beach. 
At  any  rate,  it  appears  certain  that  the  thermocline 
marks  the  lower  limit  of  the  chief  disturbing  influences 
that  act  upon  the  surface  of  the  lake.  That  it  should 
rise  with  the  progress  of  summer  is  probably  due  to  the 
increasing  stability  of  the  lower  waters,  as  differences 
in  temperature  (and  therefore  in  density)  between  upper 
and  lower  strata  are  increased.  Resistance  to  mixing 
increases  until  the  maximum  temperature  is  reached, 
and  thereafter  declines,  as  the  influence  of  cooling  and 
of  winds' penetrates  deeper  and  deeper. 

In  running  water  the  mixing  is  more  largely  mechani- 
cal, and  vertical  circulation  due  to  varying  densities  is 
less  apparent.  Yet  the  deeper  parts  of  quiet  streams 
approximate  closely  to  conditions  found  in  shallow 
lakes.  Such  thermal  stratification  as  the  current 
permits  is  direct  in  summer  and  inverse  in  winter,  and 
there  are  the  same  intervening  periods  of  thermal  over- 
turn when  the  common  temperature  approaches  40  C. 
In  summer  and  in  winter  there  is  less  "stagnation"  of 
bottom  waters  owing  to  the  current  of  the  stream. 


40  Nature  of  Aquatic  Environment 


The  thermal  conservatism  of  water — Water  is  slower 
.pond  to  changes  of  temperature  than  is  any  other 
known  substance.  Its  specific  heat  is  greater.  The 
heat  it  consumes  in  thawing  (and  liberates  in  freezing) 
is  greater.  The  am<  >unt  of  heat  necessary  to  melt  one 
part  <  >f  ice  at  0°  C.  with<  >ut  raising  its  temperature  at  all 
w<  >uld  1  >e  sufficient  to  raise  the  temperature  of  the  same 
when  melted  m<  >re  than  75  degrees.  Furthermore,  the 
heat  consumed  in  vaporization  is  still  greater.  The 
am<  >unt  required  to  vaporize  one  part  of  water  at  ioo°  C. 
without  raising  its  temperature  would  suffice  to  raise 
534  parts  <  »f  water  from  o°  C.  to  i°  C. ;  and  the  amount 
is  still  greater  when  vaporization  occurs  at  a  lower 
temperature.  Hence,  the  cooling  effect  of  evaporation 
on  the  surrounding  atmosphere,  which  gives  up  its 
heat  to  effect  this  change  of  state  in  the  water;  hence, 
the  equalizing  effect  upon  climate  of  the  presence  of 
large  bodies  of  water;  hence  the  extreme  variance 
between  day  and  night  temperatures  in  desert  lands; 
hence  the  delaying  of  winter  so  long  after  the  autumnal, 
and  of  summer  so  long  after  the  vernal  equinox. 
Water  is  the  great  stabilizer  of  temperature. 

The  content  of  natural  waters — Water  is  the  common 
solvent  of  all  foodstuffs.  These  stuffs  are,  as  every- 
body knows,  such  simple  mineral  salts  as  are  readily 
leached  out  of  the  soil,  and  such  gases  as  may  be  washed 
down  out  of  the  atmosphere.  And  since  green  plants 
are  the  producing  class  among*  organisms,  all  others 
being  dependent  on  their  constructive  activities,  water 
is  fitted  to  be  the  home  of  life  in  proportion  as  it  con- 
tains the*  essentials  of  green  plant  foods,  with  fit  condi- 
tions of  warmth,  air  and  light. 

Natural  waters  all  contain  more  or  less  of  the  elemen- 
tary foodstuffs  necessary  for  life.  Pure  water  (H20) 
is  not  found.  All  natural  waters  are  mineralized 
waters — even  rain,  as  it  falls,  is  such.    And  a  compara- 


Natural  Waters 


41 


tively  few  soluble  solids  and  gases  furnish  the  still 
smaller  number  of  chemical  elements  that  go  to  make 
up  the  living  substance.  The  amount  of  dissolved 
solids  varies  greatly,  being  least  in  rainwater,  and 
greatest  in  dead  seas,  which,  lacking  outlet,  accumulate 
salts  through  continual  evaporation.  Here  is  a  rough 
statement  of  the  dissolved  solids  in  some  typical  waters : 

In  rain  water 30 —  40  parts  per  million 

In  drainage  water  off  siliceous  soils  50 —  80  "  "       " 

In  springs  flowing  from  siliceous  soils  60 —  250  "  "       " 

In  drainage  water  off  calcareous  soils  140 —  230  "  " 
In  springs  flowing  from  calcareous 

soils   300 —  660  "  " 

In  rivers  at  large 120 —  350  "  " 

Intheocean    33000 — 37370  "  "       " 

Thus  the  content  is  seen  to  vary  with  the  nature  of 
the  soils  drained,  calcareous  holding  a  larger  portion  of 
soluble  solids  than  siliceous  soils.  It  varies  with 
presence  or  absence  of  solvents.  Drainage  waters  from 
cultivated  lands  often  contain  more  lime  salts  than  do 
springs  flowing  from  calcareous  soils  that  are  deficient 
in  carbon  dioxide.  Spring  waters  are  more  highly 
charged  than  other  drainage  waters,  because  of  pro- 
longed contact  as  ground  water  with  the  deeper  soil 
strata.  And  evaporation  concentrates  more  or  less 
the  content  of  all    impounded   waters. 

All  natural  waters  contain  suspended  solids  in  great 
variety.  These  are  least  in  amount  in  the  well  filtered 
water  of  springs,  and  greatest  in  the  water  of  turbu- 
lent streams,  flowing  through  fine  soils.  At  the  con- 
fluence of  the  muddy  Missouri  and  the  clearer 
Mississippi  rivers  the  waters  of  the  two  great  currents 
may  be  seen  flowing  together  but  uncommingled  for 
miles. 

The  suspended  solids  are  both  organic  and  inorganic, 
and  the  organic  are  both  living  and  dead,  the  latter 


±2  Nature  of  Aquatic  Environment 


being  plant  and  animal  remains.  From  all  these  non- 
living substances  the  water  tends  to  free  itself:  The 
lighter  organic  substances  (that  are  not  decomposed 
and  rediss(  Ived)  are  cast  on  shore;  the  heavier  mineral 
substances  settle  to  the  bottom.  The  rate  of  settling 
is  dependent  on  the  rate  of  movement  of  the  water  and 
on  the  specific  gravity  and  size  of  the  particles.     Fall 

kat  [thaca  gives  a  graphic  illustration  of  the  carry- 
ing p<  >wer  ( >f  the  current.  In  the  last  mile  of  its  course, 
included  between  the  Cornell  University  Campus  and 

uga  Lake,  it  sl<»\vs  down  gradually  from  a  sheer 
descent  of  78  ft.  at  the  beautiful  Ithaca  Fall  to  a  scarcely 
perceptible  current  at  the  mouth.  It  carries  huge 
1  >1<  »cks  of  stone  over  the  fall  and  drops  them  at  its  foot. 
•  •  rews  lesser  blocks  of  stone  along  its  bed  for  a  quar- 
ter ( >f  a  mile  to  a  point  where  the  surface  ceases  to  break 
in  riffles  at  low  water.  There  it  deposits  gravel,  and 
farther  along,  beds  and  bars  of  sand,  some  of  which 
shift  position  with  each  flood  rise,  and  consequent 
acceleration.  It  spreads  broad  sheets  of  silt  about  its 
m<  >uth  and  its  residual  burden  of  finer  silt  and  clay  it 
carries  out  into  the  lake.  The  lake  acts  as  a  settling 
basin.  Flood  waters  that  flow  in  turbid,  pass  out 
clear. 

Whipple  has  given  the  following  figures  for  rate  of 
settling  as  determined  by  size,  specific  gravity  and  form 
being  constant: 

Velocity  of  particles  falling   through  ivater 
leter  1.  inch,  falls  100.  feet  perminute. 

.1  "        "         8.  "      " 

.01  .15 

.001        "  -0015         "      " 

.0001      "  .000015     "      "  " 

Suspended  mineral  matters  are,  as  a  rule,  highly 
insoluble.  Instead  of  promoting,  they  lessen  the 
productivity  of  the  water  by  shutting  out  the  light. 


Gases  from  the  Atmosphere  43 

Suspended  organic  solids  likewise  contribute  nothing 
to  the  food  supply  as  long  as  they  remain  undissolved. 
But  when  they  decay  their  substance  is  restored  to 
circulation.  Only  the  dissolved  substances  that  are 
in  the  water  are  at  once  available  for  food.  The  soil 
and  the  atmosphere  are  the  great  storehouses  of  these 
materials,  and  the  sources  from  which  they  were  all 
originally  derived. 

Gases  from  the  atmosphere — The  important  gases 
derived  from  the  atmosphere  are  two :  carbon  dioxide 
(C02)  and  oxygen  (O).  Nitrogen  is  present  in  the 
atmosphere  in  great  excess  (N,  79%  to  0,  nearly  21%, 
and  C02,  .03%),  and  nitrogen  is  the  most  important 
constituent  of  living  substance,  but  in  gaseous  form, 
free  or  dissolved,  it  is  not  available  for  food.  The 
capacity  of  water  for  absorbing  these  gases  varies  with 
the  temperature  and  the  pressure,  diminishing  as 
warmth  increases  (insomuch  that  by  boiling  they  are 
removed  from  it),  and  increasing  directly  as  the  pres- 
sure increases.  Pure  water  at  a  pressure  of  760  mm.  in 
an  atmosphere  of  pure  gas,  absorbs  these  three  as 
follows : 


Oxygen 

CO2 

Nitrogen 

At    o°C 

41.14 

1796.7 

20.35 

At 2o°C 

28.38 

901.4 

14.03 

At  double  the  pressure  twice  the  quantity  of  the  gas 
would  be  dissolved.  Natural  waters  are  exposed  not 
to  the  pure  gas  but  to  the  mixture  of  gases  which  make 
up  the  atmosphere.  In  such  a  mixture  the  gases  are 
absorbed  independently  of  each  other,  and  in  propor- 
tion to  their  several  pressures,  which  vary  as  their 
several    densities:     the    following    table*    shows,    for 


*Abridged  from  a  table  of  values  to  tenths  of  a  degree  by  Birge  and  Juday 
in  Bull.  22,  Wise.  Geol.  &  Nat.  Hist.  Survey,  p.  20. 


^4  Nature  of  Aquatic  Environment 

example,  the  absorbing  power  of  pure  water  at  various 
temperatures  for  oxygen  from  the  normal  atmosphere 
at  700  mm.  pressure: 

rat    o°C    0.70  cc.  per  liter  at  i5°C    6.96  cc.  per  liter 

-  5oC    8.68cc.   "     "  "  2o°C    6.2SCC.   "     " 

-  to°C    777CC.   M     "  "   25°C    5.76CC.    M     " 

The  primary  carbon  supply  for  the  whole  organic 
world  is  the  carbon  dioxide  (C02)  of  the  atmosphere. 
Chlorophyll-bearing  plants  are  the  gatherers  o£  it. 
They  al<  >ne  among  the  organisms  are  able  to  utilize  the 
energy  of  the  sun's  rays.  The  water  existing  as  vapor 
in  the  atm<  sphere  is  the  chief  agency  for  bringing  these 
gases  down  to  earth  for  use.  Standing  water  absorbs 
them  at  its  surface  but  slowly.  Water  vapor  owing  to 
better  exposure,  absorbs  them  to  full  saturation,  and 
then  descends  as  rain.  In  fresh  water  they  are  found  in 
less  varying  proportion,  varying  from  none  at  all  to  con- 
siderable degree  of  supersaturation.  Birge  and  Juday 
report  a  maximum  occurrence  of  oxygen  as  observed  in 
the  lakes  of  Wisconsin  of  25.5  cc.  per  liter  in  Knight's 
Lake  on  Aug.  26,  1909  at  a  depth  of  4.5  meters.  This 
water  when  brought  to  the  surface  (with  consequent 
lowering  of  pressure  by  about  half  an  atmosphere) 
burst  into  lively  effervescence,  with  the  escape  of  a 
considerable  part  of  the  excess  oxygen  into  the  air. 
('l  1,  p.  52).  They  report  the  midsummer  occurrence 
of  free  carbon  dioxide  in  the  bottom  waters  of  several 
lakes  in  amounts  approaching  15  cc.  per  liter. 

The  reciprocal  relations  of  C02andO — Carbon  dioxide 
and  oxygen  play  leading  roles  in  organic  metabolism, 
albeit,  antithetic  roles.  The  process  begins  with  the 
cleavage  of  the  carbon  dioxide,  and  the  building  up  of 
its  carbon  into  organic  compounds;  it  ends  with  the 
oxidation  of  effete  carbonaceous  stuffs  and  the  reappear- 
ance of  C02.     Both  are  used  over  and  over  again. 


Carbon  Dioxide  and  Oxygen  45 

Plants  require  C02  and  animals  require  oxygen  in  order 
to  live  and  both  live  through  the  continual  exchange  of 
these  staple  commodities.  This  is  the  best  known 
phase  in  the  cycle  of  food  materials.  The  oxygen  is 
freed  at  the  beginning  of  the  synthesis  of  organic  mat- 
ter, only  to  be  recombined  with  the  carbon  at  the  end 
of  its  dissolution.  And  the  well-being  of  the  teeming 
population  of  inland  waters  is  more  dependent  on  the 
free  circulation  and  ready  exchange  of  the  dissolved 
supply  of  these  two  gases  than  on  the  getting  of  a  new 
supply  from  the  air. 

The  stock  of  these  gases  held  by  the  atmosphere  is 
inexhaustible,  but  that  contained  in  the  water  often 
runs  low;  for  diffusion  from  the  air  is  slow,  while 
consumption  is  sometimes  very  rapid.  We  often  have 
visible  evidence  of  this.  In  the  globe  in  our  win- 
dow holding  a  water  plant,  we  can  see  when  the  sun 
shines  streams  of  minute  bubbles  of  oxygen,  arising 
from  the  green  leaves.  Or,  in  a  pond  we  can  see 
great  masses  of  algae  floated  to  the  surface  on  a  foam 
of  oxygen  bubbles.  We  cannot  see  the  disappearance 
of  the  carbon  dioxide  but  if  we  test  the  water  we  find 
its  acidity  diminishing  as  the  carbon  dioxide  is  con- 
sumed. 

At  times  when  there  is  abundant  growth  of  algae  near 
the  surface  of  a  lake  there  occurs  a  most  instructive 
diurnal  ebb  and  flow  in  the  production  of  these  two 
gases.  By  day  the  well  lighted  layers  of  the  water 
become  depleted  of  their  supply  of  C02  through  the 
photosynthetic  activities  of  the  algae,  and  become 
supersaturated  with  the  liberated  oxygen.  By  night 
the  microscopic  crustaceans  and  other  plancton  animals 
rise  from  the  lower  darker  strata  to  disport  themselves 
nearer  the  surface.  These  consume  the  oxygen  and 
restore  to  the  wrater  an  abundance  of  carbon  dioxide. 
And  thus  when  conditions  are  right  and  the  numbers  of 


4  6  Nature  of  Aquatic  Environment 

plants  and  animals  properly  balanced  there  occur 
regular  diurnal  fluctuations  corresponding  to  their 
ctive  periods  of  activity  in  these  upper  strata. 
Photosynthesis  is,  however,  restricted  to  the  better 
lighted  upper  strata  of  the  water.  The  region  of 
jst  carl  m  >n  c<  msumption  is  from  one  to  three  meters 
in  depth  in  turbid  waters,  and  of  ten  meters  or  more  in 
depth  in  clear  lakes.  Consumption  of  oxygen,  however, 
onal  all  depths,  wherever  animal  respiration  or 
oic  decomposition  occurs.  And  decomposition 
<  iccurs  mi  ist  extensively  at  the  bottom  where  the  organic 
remains  tend  to  be  accumulated  by  gravity.  With  a 
complete  circulation  of  the  water  these  two  gases  may 
c<  >ntinue  to  be  used  over  and  over  again,  as  in  the  exam- 
ple just  cited.  But,  as  we  have  seen,  there  is  no  circula- 
te >n  ( >f  the  deeper  water  during  two  considerable  periods 
of  the  year;  and  during  these  stagnation  periods  the 
distribution  of  these  gases  in  depth  becomes  correlated 
in  a  wonderful  way  with  the  thermal  stratification  of 
the  water.  This  has  been  best  illustrated  by  the  work 
of  Birge  and  Juday  in  Wisconsin.  Figure  8  is  their 
diagram  illustrating  the  distribution  of  free  oxygen  in 
Mendota  Lake  during  the  summer  of  1906.  It  should 
be  studied  in  connection  writh  figure  7,  which  illustrates 
conditions  of  temperature.  Then  it  will  be  seen  that 
the  two  periods  of  equal  supply  at  all  levels  correspond 
to  vernal  and  autumnal  circulation  periods.  The 
on  opens  with  the  water  nearly  saturated  (8  cc.  of 
oxygen  per  liter  of  water)  throughout.  With  the  warm- 
ing of  the  waters  the  supply  begins  to  decline,  being 
c<  Kisumed  in  respiration  and  in  decomposition.  In  the 
upper  six  or  seven  meters  the  decline  is  not  very  exten- 
sive, f<  >r  at  these  depths  the  algae  continually  renew  the 
supply.  But  as  the  lower  strata  settle  into  their  sum- 
mer rest  their  oxygen  content  steadily  disappears,  and 
is  not  renewed  until  the  autumnal  overturn.     For  three 


Summer  Stagnation 


47 


months  there  is  no  free  oxygen  at  the  bottom  of  the 
lake,  and  during  August  there  is  not  enough  oxygen 
below  the  ten  meter  level  to  keep  a  fish  alive. 

Correspondingly,  the  amount  of  free  C02  in  the 
deeper  strata  of  the  lake  increases  rather  steadily  until 
the  autumnal  overturn.  It  is  removed  from  circulation, 
and  in  so  far  as  it  is  out  of  the  reach  of  effective  light. 
it  is  unavailable  for  plant  food. 


Fig.  8.     Dissolved  oxygen  at  different  depths  in  Lake  Mendota  in  1906.     The 
vertical  spaces  represent  cubic  centimeters  of  gas  per  liter  of  water 
the  figures  attached  to  the  curves  indicate  the  depths  in  meters.     (Birge 
and  Juday.) 

Other  gases — A  number  of  other  gases  are  more  cr 
less  constantly  present  in  the  water;  nitrogen,  as 
above  stated,  being  absorbed  from  the  air,  methane 
(CH4),  and  other  hydrocarbons,  and  hydrogen  sulphide 
(H2S),  etc.,  being  formed  in  certain  processes  of  de^om- 


±8  Nature  of  Aquatic  Environment 


position.  I  tf  these,  methane  or  marsh  gas,  is  perhaps 
the  most  important.  This  is  formed  where  organic 
matter  decays  in  absence  of  oxygen.  In  lakes  such 
c<  mditi<  >ns  are  fi  Kind  mainly  on  the  bottom.  In  marshes 
and  stagnant  shoal  waters  generally,  where  there  is 
much  accumulation  of  organic  matter  on  the  bottom, 
this  gas  is  f<  >rmed  in  abundance.  It  bubbles  up  through 
the  bottom  ooze,  or  often  buoys  up  rafts  of  agglutinated 
bottom  sediment. 

Nitrogen — The  supply  of  nitrogen  for  aquatic  organ- 
isms is  derived  from  soluble  simple  nitrates  (KN03. 
NaNOi,  etc.)  Green  plants  feed  on  these,  and  build 
proteins  out  of  them.  And  when  the  plants  die  (or 
when  animals  have  eaten  them)  their  dissolution  yields 
two  sorts  of  products,  ammonia  and  nitrates,  that 
become  again  available  for  plant  food.  Ammonia  is 
produced  early  in  the  process  of  decay  and  the  nitrates 
are  its  end  products. 

Bacteria  play  a  large  role  in  the  decomposition  of 
proteins.  At  least  four  groups  of  bacteria  successively 
participate  in  their  reduction.  The  first  of  these  are 
concerned  with  the  liquefaction  of  the  proteins,  hydroly- 
zing  the  albumins,  etc.,  by  successive  stages  to  albu- 
moses,  peptones,  etc.,  and  finally  to  ammonia.  A 
second  group  of  bacteria  oxidizes  the  ammonia  to 
nitrites.  A  third  group  oxidizes  the  nitrites  to 
nitrates.  A  fourth  group,  common  in  drainage  waters, 
reduces  nitrates  to  nitrites.  Since  these  processes  are 
g<  nng  on  side  by  side,  nitrogen  is  to  be  found  in  all 
these  states  of  combination  when  any  natural  water  is 
subjected  to  chemical  analysis.  The  following  table 
shows  some  of  the  results  of  a  large  number  (415)  of 
analyses  of  four  typical  bottomland  bodies  of  water, 
made  for  Kofoid's  investigation  of  the  plancton  of  the 
Illinois  River  by  Professor  Palmer. 


Nitrogen 

49 

ater  life  of 
of  the  table. 

The  relative  productiveness   in   open-w 
these  situations  is  shown  in  the  last  column 

In  parts 

Solids 

Free 

Ammonia 

Organic 
Nitrogen 

Nitrites 

Id, 

per  million 

Sus- 
pended 

Dis- 
solved 

Nitrates 

cm  3  per 

m3 

Illinois  River  . 
Spoon  River    . 
Quiver  Lake    . 
Thompson's  L. 

61.4 

274-3 
25.1 
44.6 

304.I 
167. 1 
248.2 
282.9 

.860 

•245 
.165 
.422 

I.03 

I.29 

.6l 

I.05 

.147 

•039 
.023 
.048 

i-59 

1. 01 

.66 

.64 

1. 91 

•39 
1.62 
6.68 

The  difference  between  these  four  adjacent  bodies  of 
water  explains  some  of  the  peculiarities  of  the  table. 
The  rivers  hold  more  solids  in  suspension  than  do  the 
lakes,  although  these  lakes  are  little  more  than  basins 
holding  impounded  river  waters.  Spoon  River  holds 
the  least  amount  of  dissolved  solids,  and  by  far  the 
greatest  amount  of  suspended  solids.  Since  the  latter 
are  not  available  for  plant  food,  naturally  this  stream 
is  least  productive  of  plancton.  Illinois  River  drains  a 
vast  and  fertile  region,  and  receives  in  its  course  the 
sewage  and  other  organic  wastes  of  two  large  cities, 
Chicago  and  Peoria,  and  of  many  smaller  ones.  Hence, 
its  high  content  of  dissolved  matter,  the  cities  being 
remote,  so  there  has  been  time  for  extensive  liquefac- 
tion. Hence,  also,  its  high  content  of  ammonia,  of 
nitrites  and  of  nitrates. 

The  two  lakes  are  very  unlike ;  Quiver  Lake  is  a  mere 
strip  of  shoal  water,  fed  by  a  clear  stream  that  flows  in 
through  low  sandy  hills.  It  receives  water  from  the 
Illinois  River  only  during  high  floods.  Thompson's 
Lake  is  a  much  larger  body  of  water,  fed  directly  from 
the  Illinois  River  through  an  open  channel.  Naturally, 
it  is  much  like  the  river  in  its  dissolved  solids,  and  in  its 
total  organic  nitrogen.  That  it  falls  far  below  the 
river  in  nitrates  and  rises  high  above  it  in  plancton 
production  may  perhaps  be  due  to  the  extensive  con- 


50 


Nature  of  Aquatic  Environment 


sumption  of  nitrates  by  plancton  algae.  Nitrates,  be- 
cause they  furnish  nitrogen  supply  in  the  form  at  once 
available  for  plant  growths,  arc,  in  shallow  waters  at 
.  an  index  of  the  fertility  of  the  water.  As  on 
land,  so  in  the  water,  the  supply  of  these  may  be 
inadr<  [uate  f<  >r  maximum  productiveness,  and  they  may 
be  added  with  profit  as  fertilizer. 

The  carbonates — Lime  and  magnesia  combine  with 
carbon  dioxide,  abstracting  it  from  the  water,  forming 


PlG.  9.     Environs  of  the  Biological  Field  Station  of  the  Illinois  State  Labora- 
tory of  Natural  History,  the  scene  of  important  work  by  Kofoid  and  others 
on  the  life  of  a  great  river. 

solid  carbonates  (CaC03  and  MgC03).  These  accumu- 
late in  quantities  in  the  shells  of  molluscs,  in  the  stems 
of  stoneworts,  in  the  incrustations  of  certain  pond 
weeds,  and  of  lime-secreting  algae.  The  remains  of 
such  organisms  accumulate  as  marl  upon  the  bottom. 
The  carbonates  (and  other  insoluble  minerals)  remain; 
the  other  body  compounds  decay  and  are  removed. 
By  such  means  in  past  geologic  ages  the  materials  for 
the  earth's  vast  deposits  of  limestone  were  accumu- 


The  Carbonates  51 


lated.  Calcareous  soils  contain  considerable  quantities 
of  these  carbonates. 

In  pure  water  these  simple  carbonates  are  practically 
insoluble ;  but  when  carbon  dioxide  is  added  to  the 
water,  they  are  transformed  into  bicarbonates*  and  are 
readily  dissolved.!  So  the  carbonates  are  leached  out 
of  the  soils  and  brought  back  into  the  water.  So  the 
solid  limestone  may  be  silently  removed,  or  hollowed  out 
in  great  caverns  by  little  underground  streams.  So 
the  Mammoth  Cave  in  Kentucky,  and  others  in  Cuba, 
in  Missouri,  in  Indiana  and  elsewhere  on  the  continent, 
have  been  formed. 

The  water  gathers  up  its  carbon  dioxide  in  part  as  it 
descends  through  the  atmosphere,  and  in  larger  part  as 
it  percolates  thru  soil  where  decomposition  is  going  on 
and  where  oxidation  products  are  added  to  it. 

Carbon  dioxide,  thus  exists  in  the  water  in  three 
conditions:  (1)  Fixed  (and  unavailable  as  plant  food) 
in  the  simple  carbonates;  (2)  "  half  -bound"  in  the 
bicarbonates;  and  (3)  free.  Water  plants  use  first  for 
food,  the  free  carbon  dioxid,  and  then  the  "half  bound" 
that  is  in  loose  combination  in  the  bicarbonates.  As 
this  is  used  up  the  simple  carbonates  are  released,  and 
the  water  becomes  alkaline. §  Birge  and  Juday  have 
several  times  found  a  great  growth  of  the  desmid 
Staurastrum  associated  with  alkalinity  due  to  this 
cause.  In  a  maximum  growth  which  occurred  in 
alkaline  waters  at  a  depth  of  three  meters  in  Devil's 
Lake,  Wisconsin,  on  June  15th,  1907,  these  plants 
numbered  176,000  per  liter  of  water. 

*CaC03,  for  example,  becoming  Ca(HC03)2,  the  added  part  of  the  formula 
representing  a  molecule  each  of  CO2  and  H20. 

flf  "hard"  water  whose  hardness  is  due  to  the  presence  of  these  bicarbonates 
be  boiled,  the  CO2  is  driven  off  and  the  simple  carbonates  are  re-precipitated  (as, 
for  example,  on  the  sides  and  bottom  of  a  tea  kettle).  This  is  "temporary 
hardness."  "Permanent  hardness"  is  due  to  the  presence  of  sulphates  and 
chlorides  of  lime  and  magnesia,  which  continue  in  solution  after  boiling. 

§Phenolphthalein,  being  used  as  indicator  of  alkalinity. 


52 


Nature  of  Aquatic  Environment 


Waters  that  are  rich  in  calcium  salts,  especially  in 
calcium  carbonate,  maintain,  as  a  rule,  a  more  abundant 
life  than  do  other  waters.  Especially  favorable  are 
they  t«  >  the  gr<  >wth  of  those  organisms  which  use  much 
lime  for  the  building  of  their  hard  parts,  as  molluscs, 
Stoneworts,  etc.  There  are,  however,  individual  pref- 
erences  in  many  of  the  larger  groups.  The  crustaceans 
for  example,  prefer,  as  a  rule,  calcium  rich  waters,  but 
one  of  them,  the  curious  entomostracan,  Holopedium 
gibberum,  (Fig.  10)  is  usually  found  in 
calcium  poor  waters,  in  lakes  in  the 
Rocky  Mountains  and  in  the  Adiron- 
< lacks,  in  waters  that  flow  off 
archaean  rocks  or  out  of  silic- 
e<  ais  sands.  The  desmids 
with  few  exceptions  are  more 
abundant  in  calcium  poor 
waters.  The  elegant  genus 
Mierasterias  is  at  Ithaca  espec- 
ially abundant  in  the  peat- 
stained  calcium-poor  waters 
of  sphagnum  bogs. 

Other  minerals  in  the  water — The  small  quantities  of 
other  mineral  substances  required  for  plant  growth  are 
furnished  mainly  by  a  few  sulphates,  phosphates  and 
chlorids:  sulphates  of  sodium,  potassium,  calcium 
and  magnesium;  phosphates  of  iron,  aluminum,  cal- 
cium and  magnesium,  and  chlorids  of  sodium,  potas- 
sium, calcium  and  magnesium.  Aluminum  alone  of 
the  elements  composing  the  above  named  compounds, 
is  not  always  requisite  for  growth,  although  it  is  very 
often  present.  Silica,  likewise,  is  of  wide  distribution, 
and  occurs  in  the  wrater  in  considerable  amounts,  and 
is  used  by  many  organisms  in  the  growth  of  their  hard 
parts.  As  the  stoneworts  use  lime  for  their  growth, 
some  4r ;   of  the  dry  weight  of  Chara  being   CaO,   so 


f 

Fig.  io.  A  gelatinous-coated  mi- 
crocrustacean,  Holopedium  gib- 
ber um,  often  found  in  waters 
that  are  poor  in  calcium. 


Mineral  Content 


53 


diatoms  require  silica  to  build  their  shells.  When  the 
diatoms  are  dead  their  shells,  relatively  heavy  though 
extremely  minute,  slowly  settle  to  the  bottom,  slowly 
dissolving;  and  so,  analyses  of  lake  waters  taken  at 
different  depths  usually  show  increase  of  silica  toward 
the  bottom. 

Iron,  common  salt, 
sulphur,  etc.,  often 
occur  locally  in  great 
abundance,  notably  in 
springs  flowing  from 
special  deposits,  and 
when  they  occur  they 
possess  a  fauna  and 
flora  of  marked  pecu- 
liarities and  very 
limited  extent. 

An  idea  of  the  rela- 
tive abundance  of  the 
commoner  mineral 
substances  in  lake 
waters  may  be  had 
from  the  following 
figures  that  are  con- 
densed from  Birge  and 
Juday's  report  of  74 
analyses. 


Fig.  11.     A  beautiful  green  desmid,  Micra- 
sterias  that  is  common  in  bog  waters. 


MINERAL    CONTENT    OF    WISCONSIN    LAKES 
Parts  per  million 
FI2O3  + 


Si02 
Minimum      0.8 
Maximum  33.0 

AI3O3     Ca 

0.4      0.6 

11. 2    49.6 

Mg 
0.3 

32.7 

Na      K 
0.3    0.3 
6.2    3.1 

C03 

0.0 
12.0 

HCO3 

4-9 
IS3-0 

S04 

0.0 

18.7 

CI 

10. 0 

Average       1 1 . 7 

2.1    26.9 

19.6 

3.2     2.2 

2.1 

91.7 

9.8 

39 

This  is  the  bill  of  fare  from  which  green  water  plants 
may  choose.     Forel  aptly  compared  the  waters  of  a 


54  Nature  of  Aquatic  Environment 

lake  to  the  blood  of  the  animal  body.  As  the  cells  of 
the  body  take  from  the  Mood  such  of  its  content  as  is 
suited  to  their  need,  so  the  plants  and  animals  of  the 
water  renew  their  substance  out  of  the  dissolved  sub- 
tin-  water  brings  to  them. 

ante  substances  dissolved  in  the  water  may  so 
i  I  n  »tli  its  density  and  its  viscosity  as  to  determine 
both  stratification  and  distribution  of  suspended  solids. 
This  is  a  matter  that  has  scarcely  been  noticed  by 
limnologists  hitherto.  Dr.  J.  U.  Lloyd  ('82)  long  ago 
sin  wed  how  by  the  addition  of  colloidal  substances  to  a 
vessel  of  water  the  whole  contents  of  the  vessel  can  be 
1  >r<  >ken  into  strata  and  these  made  to  circulate,  each  at 
its  own  level,  independent  of  the  other  strata.  Solids 
in  suspension  can  be  made  to  float  at  the  top  of  particu- 
lar strata,  according  to  density  and  surface  tension. 

Perhaps  the  "false  bottom"  observed  in  some  north- 
ern bog-bordered  lakes  is  due  to  the  dissolved  colloids 
of  the  stratum  on  which  it  floats.  Holt  ('08,  p.  219) 
ribes  the  "false  bottom"  in  Sumner  Lake,  Isle 
R<  >yal,  as  lying  six  to  ten  feet  below  the  surface,  many 
f<  ■  t  above  the  true  bottom;  as  being  so  tenuous  that  a 
p<  >le  could  be  thrust  through  it  almost  as  readily  as 
through  clear  water;  and  as  being  composed  of  fine 
disintegrated  remains  of  leaves  and  other  light  organic 
material.  "In  places  there  were  great  breaks  in  the 
'false  bottom,'  doubtless  due  to  the  escape  of  gases 
which  had  lifted  this  fine  ooze-like  material  from  a 
greater  depth:  and  through  these  breaks  one  could 
look  down  several  feet  through  the  brownish  colored 
water." 

Perhaps  the  colloidal  substances  in  solution  are 
such  as  harden  upon  the  surface  of  dried  peat,  like  a 
water-proof  glue,  making  it  for  a  time  afterward  imper- 
vious to  water. 


*     :^f 

s  -  r. 

^1 

if--.;   •« 

sN- 

?iiNv  ?-iN 

as* 

airy! 

rr* 

v* 
>- 

■E^P^Wfl 

V  fl 

.-  -    r_  ;.           J 

s] 

1  * 

2 

& 

l&*^ 

£ 

-  ^" 

r  •  ^ssfe. 

:-*.   — -* 

WATER   AND 

LAND 

CEANS  are  the  earth's 
great  storehouse  of  water. 
They  cover  some  eight- 
elevenths  of  the  surface 
of  the  earth  to  an  average 
depth  of  about  two  miles. 
They  receive  the  off-flow 
from  all  the  continents 
and  send  it  back  by  way 
of  the  atmosphere. 
The  fresh  waters  of  the  earth  descend  in  the  first 
instance  out  of  the  atmosphere.  They  rise  in  vapor 
from  the  whole  surface  of  the  earth,  but  chiefly  from 
the  ocean.  Evaporation  frees  them  from  the  ocean's 
salts,  these  being  non- volatile.  They  drift  about  with 
the  currents  of  the  atmosphere,  gathering  its  gases  to 
saturation,  together  with  very  small  quantities  of  drift- 
ing solids;  they  descend  impartially  upon  water  and 
land,  chiefly  as  rain,  snow  and  hail. 

They  are  not  distributed  uniformly  over  the  face  of 
the  continents  for  each  continent  has  its  humid  regions 
and  its  deserts.  Rainfall  in  the  United  States  varies 
from  5  to  ioo  inches  per  annum.  Two-thirds  of  it 
falls  on  the  eastern  three-fifths  of  the  country.  For  the 
Eastern  United  States  it  averages  about  48  inches,  for 
the  Western  United  States  about  12  inches;  the  average 
for  the  whole  is  about  30  inches.  The  total  annual 
precipitation  is  about  5,000,000,000  acre-feet.* 

*An  acre-foot  is  an  acre  of  water  I  foot  deep  or  43,560  cubic  feet  of  water. 

55 


Water  and  Land 


It  is  commonly  estimated  that  at  least  one-half  of 
this  rainfall  is  evaporated,  in  part  from  soil  and  water 
surfaces,  but  much  more  from  growing  vegetation;  for 
the  transpiration  of  plants  gives  back  immense  quanti- 
i  £  water  to  the  atmosphere.  Hellriegel  long  ago 
ed  that  a  crop  of  corn  requires  300  tons  of  water 
■iv :  of  potatoes  or  clover,  400  tons  per  acre.  At 
the  I<  >wa  Agricultural  Experiment  Station  it  was  shown 
that  an  acre  of  pasturage  requires  3,223  tons  of  water, 
( ,r  28  inches  in  depth  (2}i  acre-feet).  Before  the  days 
of  tile  drainage  it  was  a  not  uncommon  practice  to 
plant  will*  w  trees  by  the  edges  of  swales,  in  order  that 
they  might  carry  off  the  water  through  their  leaves, 
leaving  the  ground  dry  enough  for  summer  cropping. 
The  rate  of  evaporation  is  accelerated  also,  by  high 
temperatures  and  strong  winds. 

The  rain  tends  to  wet  the  face  of  the  ground  every- 
where. How  long  it  will  stay  wet  in  any  given  place 
will  depend  on  topography  and  on  the  character  of  the 
s<  ol  as  well  as  on  temperature  and  air  currents.  Show- 
ers descending  intermittently  leave  intervals  for  com- 
plete run-off  of  water  from  the  higher  ground,  with 
ort unity  for  the  gases  of  the  atmosphere  to  enter 
and  do  their  work  of  corrosion.  The  dryer  intervals, 
therefore,  are  times  of  preparation  of  the  materials 
that  will  appear  later  in  soil  waters.  Yet  all  soils  in 
humid  regions  retain  sufficient  moisture  to  support  a 
c<  >nsiderable  algal  flora.  Periodical  excesses  of  rainfall 
are  necessary  also  to  maintain  the  reserve  of  ground 
water  in  the  soil.  Suppose,  for  example,  that  the  35 
inches  of  annual  rainfall  at  Ithaca  were  uniformly 
distributed.  There  would  be  less  than  one-tenth  of  an 
inch  of  precipitation  each  day — an  amount  that  would 
I  e  quiddy  and  entirely  evaporated,  and  the  ground 
would  never  be  thoroughly  wet  and  there  would  be  no 
gr<  >und  water  to  replenish  the  streams.     Storm  waters 


Soil  and  Stream-flow  57 

tend  to  be  gathered  together  in  streams,  and  thus  about 
one-third  of  our  rainfall  runs  away.  In  humid  areas 
small  streams  converge  to  form  larger  ones,  and  flow 
onward  to  the  seas.  In  arid  regions  they  tend  to 
spread  out  in  sheet  floods,  and  to  disappear  in  the  sands. 

In  a  state  of  nature  little  rain  water  runs  over  the 
surface  of  the  ground,  apart  from  streams.  It  mainly 
descends  into  the  soil.  How  much  the  soil  can  hold 
depends  upon  its  composition.  Dried  soils  have  a 
capacity  for  taking  up  and  holding  water  about  as  fol- 
lows: sharp  sand  25%,  loam  50%,  clay  60%,  garden 
mould  90%  and  humus  1 80%  of  their  dry  weight .  Water 
descends  most  rapidly  through  sand  and  stands  longest 
upon  the  surface  of  pure  clay.  Thick  vegetation  with 
abundant  leaf  fall,  and  humus  in  the  soil  tend  to  hinder 
run-off  of  storm  waters,  and  to  prolong  their  passage 
through  the  soil.  Thus  the  excess  of  rainfall  is  gradually 
fed  into  the  streams  by  springs  and  seepage.  Under 
natural  conditions  streams  are  usually  clear,  and  their 
flow  is  fairly  uniform. 

Unwise  clearing  of  the  land  and  negligent  cultivation 
of  the  soil  facilitate  the  run-off  of  the  water  before  the 
storm  is  well  spent,  promote  excessive  erosion  and 
render  the  streams  turbid  and  their  volume  abnormally 
fluctuating.  Little  water  enters  the  soil  and  hence  the 
springs  dry  up,  and  the  brooks,  also,  as  the  seepage  of 
ground  water  ceases.  Two  great  evils  immediately 
befall  the  creatures  that  live  in  the  streams  and  pools : 
( 1 )  There  is  wholesale  direct  extermination  of  them  with 
the  restriction  of  their  habitat  at  low  water.  (2)  There 
occurs  smothering  of  them  under  deposits  of  sediment 
brought  down  in  time  of  floods,  with  indirect  injury  to 
organisms  not  smothered,  due  to  the  damage  to  their 
foraging  grounds. 

The  waters  of  normal  streams  are  derived  mainly 
from  seepage,  maintained  by  the  store  of  water  accumu- 


;8  Water  and  Land 


lated  in  the  soil.  This  store  of  ground  water  amounts 
according  to  recent  estimates  to  some  25%  of  the  bulk 
e  first  one  hundred  feet  in  soil  depth.  Thus  it 
equals  a  reservoir  of  water  some  25  feet  deep  covering 
the  whole  humid  eastern  United  States.  It  is  con- 
tinuous over  the  entire  country.  Its  fluctuations  are 
studied  by  means  of  measurements  of  wells,  especially 
recording  the  depth  of  the  so-called  "water  table." 
(  hi  the  maintenance  of  ground  water  stream-flow  and 
organic  productiveness  of  the  fields  alike  depend. 


CHAPTER  III 


TYPES   OF  AQUATIC 
ENVIRONMENT 


LAKES   AND 
PONDS 


UT  of  the  atmosphere 
comes  our  water  supply 
— the  greatest  of  our 
natural  resources.  It 
falls  on  hill  and  dale, 
and  mostly  descends 
into  the  soil.  The  ex- 
cess off -flowing  from  the 
surface  and  outflowing  from  springs  and  seepage,  forms 
water  masses  of  various  sorts  according  to  the  topog- 
raphy of  the  land  surface.  It  forms  lakes,  streams  or 
marshes  according  as  there  occur  basins,  channels  or 
only  plant  accumulations  influencing  drainage. 

The  largest  of  the  bodies  of  water  thus  formed  are 
the  lakes.  Our  continent  is  richly  supplied  with  them, 
but  they  are  of  very  unequal  distribution.  The  lake 
regions  in  America  as  elsewhere  are  regions  of  compara- 
tively recent  geological  disturbance.  Lakes  thickly 
dot  the  peninsula  of  Florida,  the  part  of  our  continent 
most  recently  lifted  from  the  sea.  Over  the  northern 
recently    glaciated    part    of    the    continent    they    are 

59 


6o  Types  of  Aquatic  Environment 


innumerable,  but  in  the  great  belts  of  corn  and  cotton, 
and  on  the  plains  to  the  westward,  they  are  few  and 
far  1  >etween.  They  are  abundant  in  the  regions  of  more 
recent  volcanic  disturbance  in  our  western  mountains, 
but  are  practically  absent  from  the  geologically  older 
Appalachian  hills.  They  lie  in  the  depressions  between 
the  recently  uplifted  lava  blocks  of  southern  Oregon. 
They  occur  also  in  the  craters  of  extinct  volcanoes. 
They  are  apt  to  be  most  picturesque  when  their  setting 
is  in  the  midst  of  mountains.  There  are  probably  no 
more  1  >eautiful  lakes  in  the  world  than  some  of  those  in 
the  West,  such  as  Lake  Tahoe  (altitude  6200  ft.)  on  the 
California-Nevada  boundary,  and  Lake  Chelan  in  the 
state  of  Washington*,  to  say  nothing  of  the  Coeur 
d'Alene  in  Idaho  and  Lake  Louise  in  British  Columbia. 
Eastward  the  famous  lake  regions  that  attract  most 
visitors  are  those  of  the  mountains  of  New  York  and 
New  England,  those  of  the  woodlands  of  Michigan  and 
Wisconsin  and  those  of  the  vast  areas  of  rocks  and  water 
in  Canada. 

Lakes  are  temporary  phenomena  from  the  geologists 
point  of  view.  No  sooner  are  their  basins  formed  than 
the  work  of  their  destruction  begins.  Water  is  the 
agent  of  it,  gravity  the  force  employed,  and  erosion 
the  chief  method.  Consequently,  other  things  being 
equal,  the  processes  of  destruction  go  on  most  rapidly 
in  regions  of  abundant  rainfall.  Inwash  of  silt  from 
surrounding  slopes  tends  to  fill  up  their  ba  ins.  The 
most  extensive  filling  is  about  the  mouths  of  inflowing 
stnams,  where  mud  flats  form,  and  extend  in  Deltas 
out  into  the  lake.  These  deltas  are  the  exposed  sum- 
mits of  great  mounds  of  silt  that  spread  out  broadly 
underneath  the  water  on  the  lake  floor.  At  the  shore- 
lines these  deposits  are  loosened  by  the  frosts  of  winter, 

*Descriptions  of  these  two  lakes  will  be  found  in  Russell's  Lakes  of  North 
i  ica. 


Lakes  Temporary  Phenomena 


61 


pushed  about  by  the  ice  floes  of  spring,  and  scattered 
by  every  summer  storm,  but  after  every  shift  they  set- 
tle again  at  lower  levels.  Always  they  are  advancing 
and  filling  the  lake  basin.  The  filling  may  seem  slow 
and  insignificant  on  the  shore  of  one  of  the  Great  Lakes 
but  its  progress  is  obvious  in  a  mill  pond,  and  the  dif- 
ference is  only  relative. 


"1 


& 


Fig.  12.  An  eroding  bluff  on  the  shore  of  Lake  Michigan  that  is  receding  at 
the  rate  of  several  feet  each  year.  The  broad  shelving  beach  in  the  fore- 
ground is  sand,  where  the  waves  ordinarily  play.  Against  the  bare  rising 
boulder-strewn  strip  back  of  this,  the  waves  beat  in  storms;  at  its  summit 
they  gather  the  earth-slides  from  the  bank  above  and  carry  them  out  into 
the  lake.  The  black  strip  at  the  rear  of  the  sand  is  a  line  of  insect  drift, 
deposited  at  the  close  of  a  midsummer  storm  by  the  turning  of  the  wind  on 
shore. 


On  the  other  hand,  lakes  disappear  with  the  cutting 
down  of  the  rim  of  their  basins  in  outflow  channels.  The 
Niagara  river,  for  example,  is  cutting  through  the  lime- 


62 


Types  of  Aquatic  Environment 


stone  barrier  that  retains  Lake  Erie.  At  Niagara 
Falls  it  is  making  progress  at  the  rate  of  about  five  feet 
a  year.  Since  the  glacial  period  it  has  cut  back  from 
the  shore  of  Lake  ( Ontario  a  distance  of  some  seventeen 
miles,  and  if  the  orocess  continues  it  wil  in 
empty  Lake  Erie. 


pr 


Fig.  13.    Evans'  Lake,  Michigan;  a  lake  in  process  of  being  filled  by  encroach- 
ment of  plants.     A  line  of  swamp  loose-strife  (Decodon)  leads  the  invading 
shore  vegetation.    Further  in  wash  of  silt  or  lowering  of  outlet  is  precluded 
■  usity  of  the  surrounding  heath.     The  plants  control  its  fate. 

Photo  by  E.  McDonald. 

When  the  glacier  lay  across  the  St.  Lawrence  valley, 
before  it  had  retreated  to  the  northward,  all  the  waters 
of  the  great  lakes  region  found  their  way  to  the  ocean 
t  hr<  nigh  the  A I  <  >hawk  Valley  and  the  Hudson.  At  that 
time  a  similar  process  of  cutting  an  outlet  through  a 
linn-stone  barrier  was  going  on  near  the  site  of  the 
present  village  of  Jamesville,  New  York,  where  on  the 


The  Great  Lakes 


63 


Clark  Reservation  one  may  see  today  a  series  of 
abandoned  cataracts,  dry  rock  channels  and  plunge 
basins.  Green  Lake  at  present  occupies  one  of  these 
old  plunge  basins,  its  waters,  perhaps  a  hundred  feet 
deep,  are  surrounded  on  all  sides  but  one,  by  sheer 
limestone  cliffs  nearly  two  hundred  feet  high. 

When  lakes  become  populated  then  the  plants  and 
animals  living  in  the  water  and  about  the  shore  line 
contribute  their  remains  to  the  final  filling  of  the  basin. 
This  is  well  shown  in  figure  13. 

The  Great  Lakes  con- 
stitute the  most  magnifi- 
cent system  of  reservoirs 
of  fresh  water  in  the  world ; 
five  vast  inland  seas, 
whose  shores  have  all  the 
sweep  and  majesty  of  the 
ocean,  no  land  being  visi- 
ble across  them.  All  but 
one  (Erie)  have  the  bot- 
tom of  their  basins  below 
the  sea  level.  Their  area, 
elevation  and  depth  are 
as  follows: 


Area  in 
sq.  mi. 

Lake  Ontario    7.240 

Erie    9.960 

"     Huron*    23.800 

"     Michigan 22.450 

"     Superior 31.200 

*Including  Georgian  Bay. 
t  Approximate. 

They  are  stated  by  Russell  to  contain  enough  water 
to  keep  a  Niagara  full-flowing  for  a  hundred  years. 


The  larger  lakes  and  i 

-ivers  of 

North  America. 

Surface 

Depth 

in  feet 

alt. in  ft. 

meanf  i 

naximum 

247 

300 

738 

573 

70 

210 

581 

250 

730 

581 

325 

S70 

602 

475 

1.00S 

64  Types  of  Aquatic  Environment 

The  Finger  Lukes  of  the  Seneca  basin  in  Central  New 
York  constitute  an  unique  series  occupying  one  section 
of  the  drainage  area  of  Lake  Ontario,  with  which  they 
communicate  by  the  Seneca  and  Oswego  rivers.  They 
occupy  deep  and  narrow  valleys  in  an  upland  plateau 
^{  soft  Devonian  shales.  Their  shores  are  rocky  and 
increasingly  precipitous  near  their  southern  ends.  The 
marks  of  glaciation  are  over  all  of  them.  Keuka,  the 
most  picturesque  of  the  series,  occupies  a  forking  valley 
partially  surrounding  a  magnificent  ice- worn  hill. 
The  others  are  all  long  and  narrow  and  evenly  contoured, 
without  islands  (save  for  a  single  rocky  islet  near  the 
east   Cayuga  shore)   or  bays. 

The  basins  of  these  lakes  invade  the  high  hills  to  the 
southward,  reaching  almost  to  the  head- waters  of 
the  tributaries  of  the  Susquehanna  River.  Here 
there  is  found  a  wonderful  diversity  of  aquatic  situa- 
tion. At  the  head  of  Cayuga  Lake,  for  example, 
1  »ey<  >nd  the  deep  water  there  is  a  mile  of  broad  shelving 
silt -covered  lake  bottom,  ending  in  a  barrier  reef. 
Then  there  is  a  broad  flood  plain,  traversed  by  deep 
slow  meandering  streams,  and  covered  in  part  by 
marshes.  Then  come  the  hills,  intersected  by  narrow 
post-glacial  gorges,  down  which  dash  clear  streams 
in  numerous  beautiful  waterfalls  and  rapids.  Back 
of  the  first  rise  of  the  hills  the  streams  descend  more 
slowly,  gliding  along  over  pebbly  beds  in  shining 
riffles,  or  loitering  in  leaf-strewn  woodland  pools. 
A  few  miles  farther  inland  they  find  their  sources  in 
alder-bordered  brooks  flowing  from  sphagnum  bogs  and 
upland  swales  and  springs. 

Tims  the  waters  that  feed  the  Finger  Lakes  are 
all  derived  from  sources  that  yield  little  aquatic 
life,  and  they  run  a  short  and  rapid  course  among 
the  hills,  with  little  time  for  increase  by  breeding: 
hence  they  contribute  little  to  the  population  of  the 


The  Finger  Lakes 


65 


lake.  They  bring 
of  food  materials, 
hills. 

Bordering  the  Finger  Lakes 
marshes,  save  at  the  ends 
of  Cayuga,  and  the  chief 
irregularities  of  outline 
are  formed  by  the  deltas 
of  inflowing  streams. 
The  two  large  central 
lakes,  Cayuga  and  Sen- 
eca, have  their  basins 
extending  below  the  sea 
level.  Their  sides  are 
bordered  by  two  steeply- 
rising,  smoothly  eroded 
hills  of  uniform  height, 
between  which  they  lie 
extended  like  wide  placid 
rivers.  The  areas,  eleva- 
tions and  depths  of  the 
five  are  as  follows: 


in  constantly,  however,    a   supply 
dissolved    from    the    soils    of    the 


there  are  no  extensive 


Fig.  15.     The  Finger  Lakes  of  Central 
New  York. 

A,  Canandaigua;  B,  Keuka;  C,  Seneca;  D, 
Cayuga;  E.Owasco;  F,  Skaneateies;  G,  Otisco; 
H,  the  Seneca  River;  I,  The  arrow  indicates  the 
location  of  the  Cornell  University  Biological 
Field  Station  at  Ithaca.  The  stippled  area  at 
the  opposite  end  of  "Cayuga  Lake  marks  the 
location  of  the  Montezuma   Marshes. 


Lake  Skaneateies 
Owasco 
Cayuga    .  . . 
Seneca   . . . . 


Area 

Surface 

Depth 

in  feet 

sq.  mi. 

alt.  in  ft. 

mean     maximum 

*3-9 

S67 

142 

297 

10.3 

710 

5 

177 

66.4 

38l 

^77 

435 

67.7 

444 

288 

618 

18. 1 

709 

99 

183 

16.3 

686 

126 

274 

Keuka    18. 1 

Canandaigua 

Birge  and  Juday  found  the  transparency  of  four  of 
these  lakes  as  measured  by  Secchi's  disc  in  August,  19 10, 
to  be  as  follows: 

Canandaigua    12.0  ft.         Seneca 27.0  ft. 

Cayuga   16.6  ft.         Skaneateies 33.5  ft. 


66 


Types  of  Aquatic  Environment 


The  Takes  of  the  Yahara  Valley  in  Southern  Wisconsin 
are  of  an<  >ther  type.  They  occupy  broad,  shallow  basins 
formed  by   the  deposition   of  barriers  of  glacial  drift 

in  the  preglacial  course  of 
the  Yahara  River.  Their 
outlet  is  through  Rock 
River  into  the  Missis- 
sippi. Their  shores  are 
indented  with  numerous 
bays,  and  bordered  ex- 
tensively by  marshes. 
The  surrounding  plain  is 
dotted  with  low  rounded 
hills,  some  of  which  rise 
abruptly  from  the  water, 
making  attractive  shores. 
The  city  of  Madison  is 
the  location  of  the  Uni- 
versity of  Wisconsin , 
which  Professor  Birge  has 
made  the  center  of  the 
most  extensive  and  care- 
ful study  of  lakes  yet 
undertaken  in  America. 
The  area,  elevation  and 
depth  of  these  lakes  is  as 
follows : 


Fig.   i  6.     The  four-lake   region  of 
Madison,  Wisconsin. 


Lake  Ke^onsa 
"    Wabi 

Monona 

"     Mr- 


Area  in 

Surface 

Depth  in  feet 

sq.  mi. 

alt.  in  ft. 

mean 

maximum 

15 

842 

15 

31 

3 

844 

15 

36 

6 

845 

27 

75 

15 

849 

40 

85 

Floodplain  Lakes  67 


Lakes  resulting  from  Erosion — Although  erosion  tends 
generally  to  destroy  lakes  by  eliminating  their  basins, 
here  and  there  it  tends  to  foster  other  lakes  by  making 
basins  for  them.  Such  lakes,  however,  are  shallow  and 
fluctuating.  They  are  of  two  very  different  sorts, 
floodplain  lakes  and  solution  lakes. 

Floodplain  Lakes  and  Ponds — Basins  are  formed  in 
the  floodplains  of  rivers  by  the  deposition  of  barriers 
of  eroded  silt,  in  three  different  ways. 

1 .  By  the  deposition  across  the  channel  of  some  large 
stream  of  the  detritus  from  a  heavily  silt-laden  tributary 
stream.  This  blocks  the  larger  stream  as  with  a  partial 
dam,  creating  a  lake  that  is  obviously  but  a  dilatation 
of  the  larger  stream.  Such  is  Lake  Pepin  in  the 
Mississippi  River,  created  by  the  barrier  that  is  de- 
posited by  the  Chippewa  River  at  its  mouth. 

2.  By  the  partial  filling  up  of  the  abandoned  chan- 
nels of  rivers  where  they  meander  through  broad 
alluvial  bottom-lands.  Phelps  Lake  partly  shown  in 
the  figure  on  page  50  is  an  example  of  a  lake  so  formed ; 
and  all  the  other  lakes  of  that  figure  are  partly  occluded 
by  similar  deposits  of  river  silt.  Horseshoe  bends  are 
common  in  slow  streams,  and  frequently  a  river  will  cut 
across  a  bend,  shortening  its  course  and  opening  a 
new  channel ;  the  filling  up  with  silt  of  the  ends  of  the 
abandoned  channel  results  in  the  formation  of  an  "ox- 
bow" lake;  such  lakes  are  common  along  the  lower 
course  of  the  Mississippi,  as  one  may  see  by  consult- 
ing any  good  atlas. 

3.  By  the  deposition  in  times  of  high  floods  of  the 
bulk  of  its  load  of  detritus  at  the  very  end  of  its  course, 
where  it  spreads  out  in  the  form  of  a  delta.  Thus  a 
barrier  is  often  formed  on  one  or  both  sides,  encircling  a 
broad  shallow  basin.  Such  is  Lake  Pontchartrain  at 
the  left  of  the  ever  extending  delta  of  the  Mississippi. 


68 


Types  of  Aquatic  Environment 


Solution  Lakes  and  Ponds— Of  very  different  charac- 
ter are  the  lakes  whose  basins  are  produced  by  the 
dissolution  pf  limestone  strata  and  the  descent  of  the 
■  verlying  s<  >il  in  the  form  of  a  "sink."  This  is  erosion, 
not  by  mechanical  means  at  first,  but  by  solution.     It 

( »ccurs  where  beds  of  soluble  strata 
lie  above  the  permanent  ground 
water  level,  and  are  themselves 
overlaid  by  clay.  Rain  water 
falling  through  the  air  gathers 
carbon  dioxide  and  becomes  a 
solvent  of  limestone.  Percolat- 
ing downward  through  the  soil  it 
passes  through  the  permeable 
carbonate,  dissolving  it  and 
carrying  its  substance  in  solution 
to  lower  levels,  of  ten  flowing  out 
in  springs.  As  the  limestone  is 
thus  removed  the  superincum- 
bent soil  falls  in,  forming  a  sink 
hole.  The  widening  of  the  hole, 
by  further  solution  and  slides 
results  in  the  formation  of  the 
pond  or  lake,  possibly,  at  the 
beginning,  as  a  mere  pool. 

The  area  of  such  a  lake  is  doubtless  gradual  el 
increased  by  the  settling  of  the  bottom  around  thy 
sink  as  the  soluble  limestone  below  is  slowly  carried 
away.  Its  configuration  is  in  part  determined  by  the 
original  topography  of  the  land  surface,  and  in  part  by 
the  course  of  the  streamflow  underground :  but  its  bed 
is  unique  among  lake  bottoms  in  that  all  its  broad 
shoals  suddenly  terminate  in  one  or  more  deep  funnel- 
shaped  outflow  depressions. 

Lime  sinks  occur  ( >ver  considerable  areas  in  the  south 
ern  stato  is,  and  in  those  of  the  Ohio  Valley,  but  perhaps 


Fig.  17.  Solution  lakes  of 
□  County,  Florida, 
■■■:    Sellards). 

The  white  spots  in  the  lakes  indi- 
cate sinks 

A.  Lake  Iamonia;    area  at  high 

ro  sq.  mi. 

B.  Lake  Jackson;   area   7  sq.  mi. 

C.  Lake     Fafayette;     area  3K 
sq.  mi. 

D.  Lake  Miccosukee;  are  a  7?  sq. 
mi.;  depth  of  north  sink  28  ft. 
Water  escapes  through  this  sink 
at  the  estimated  rate  of  1000 
gals,  per  minute. 

klockr.ee      River;    S,    St 
River;    T,   Tallahassee. 


Solution   Lakes 


69 


the  best  development  of  lakes  about  them  is  in  the 
upland  region  of  northern  Florida.  These  lakes  are 
shallow  basins  having  much  of  their  borders  ill-defined 
and  swampy.  Perhaps  the 
most  remarkable  of  them  is 
Lake  Alachua  near  Gaines- 
ville. At  high  water  this 
lake  has  an  area  of  some 
twenty-five  square  miles  and 
a  depth  (outside  the  sink)  of 
from  two  to  fourteen  feet. 
At  its  lowest  known  stage  it 
is  reduced  to  pools  filling 
the  sinks.  During  its  re- 
corded history  it  has  several 
times  alternated  between 
these  conditions.  It  has 
been  for  years  a  vast  ex- 
panse of  water  carrying 
steamboat  traffic,  and  it  has 
been  for  other  years  a  broad 
grassy  plain,  with  no  water 
in  sight.  The  widening  or 
the  stoppage  of  the  sinks 
combined  with  excessive  or 
scanty  rainfall  have  been 
the  causes  of  these  remark- 
able changes  of  level. 

The  sinks  are  more  or 
less  funnel-shaped  openings 
leading  down  through  the  soil  into  the  limestone. 
Ditchlike  channels  often  lead  into  them  across  the  lake's 
bottom.  The  accompanying  diagram  shows  that  they 
are  sometimes  situated  outside  the  lake's  border,  and 
suggest  that  such  lakes  may  originate  through  the 
formation  of  sinks  in  the  bed  of  a  slow  stream. 


Fig.  18.  Lake  Miccosukee,  (after 
Sellarcls),  showing  sinks;  one  in 
lake  bottom  at  north  end,  two  in 
outflowing  stream,  2}i  miles  dis- 
tant. Arrows  indicate  normal 
direction  of  stream  flow,  (reversed 
south  of  sinks  in  flood  time  when 
run-off  is  into  St.  Mark's  River). 


jo  Types  of  Aquatic  Environment 

Such  lakes,  when  their  basins  lie  above  the  level  of 
the  permanent  water  table,  may  sometimes  be  drained 
jinking  wells  through  the  soil  of  their  beds.  This 
allows  the  escape  of  their  waters  into  the  underlying 
limestone.  Sometimes  they  drain  themselves  through 
the  widening  of  their  underground  water  channels. 
Always  they  are  subject  to  great  changes  of  level  conse- 
quent upon  variation  in  rainfall. 

En<  >ugh  examples  have  now  been  cited  to  show  how 
great  diversity  there  is  among  the  fresh-water  lakes  of 
N<  >rth  America.  Among  those  we  have  mentioned  are 
the  lakes  that  have  received  the  most  attention  from 
limnologists  hitherto ;  but  hardly  more  than  a  beginning 
has  been  made  in  the  study  of  any  of  them.  Icthyolo- 
gists  have  collected  fishes  from  most  of  the  lakes  of  the 
entire  continent,  and  plancton  collections  have  been 
made  from  a  number  of  the  more  typical :  from  Yellow- 
stone Lake  by  Professor  Forbes  in  1890  and  from  many 
other  lakes,  rivers  and  cave  streams  since  that  date. 

Lakeside  laboratories — On  the  lakes  above  mentioned 
are  located  a  number  of  biological  field  stations.  That 
at  Cornell  University  is  at  the  head  of  Cayuga  Lake. 
That  of  the  Ohio  State  University  is  at  Sandusky  on 
Lake  Erie.  The  Canadian  fresh-water  station  is  at  Go 
Home  Bay  on  Lake  Huron.  The  biological  laboratories 
of  the  University  of  Wisconsin  are  located  directly  upon 
the  shore  of  Lake  Mendota.  Other  lakeside  stations 
are  as  follows: 

That  of  the  University  of  Michigan  is  on  Douglas 
Lake  in  the  northern  end  of  the  southern  peninsula  of 
Michigan.  This  is  an  attractive  sheet  of  water  at  an 
altitude  of  712  ft.,  covering  an  area  of  5.13  square  miles, 
and  having  (as  far  as  surveyed)  a  maximum  depth  of 
89  feet  and  an  average  depth  of  22  feet.  Its  transpar- 
ency by  Secchi's  disc  as  measured  in  August  is  about 
four  meters. 


Depth   and  Breadth 


That  of  the  University  of  Indiana  is  on  Winona 
Lake,  a  shallow  hard  water  lake  of  irregular  outline, 
having  an  area  of  something  less  than  a  square  mile, 
an  elevation  of  810  feet,  a  maximum  depth  of  81  feet 
and  a  transparency  (Secchi's  disc)  varying  with  the 
season  between  7  and  15  feet. 

That  of  the  University  of  Iowa  is  on  Okoboji  Lake. 

That  of  the  University  of  North  Dakota  is  on  Devils 
Lake,  an  alkaline  upland  lake  (salinity  1%)  having  an 
area  of  62J/Z  square  miles  and  a  maximum  depth  of  25 
feet.  The  salt-marsh  ditch-grass  {Ruppia  maritima) 
is  the  only  seed  plant  growing  in  its  waters. 

That  of  the  University  of  Montana  is  on  Flathead 
Lake,  a  cold  mountain  lake  some  thirty  miles  long  by 
ten  miles  broad  having  an  elevation  of  2916  ft.  and  a 
maximum  depth  of  280  ft. 

That  of  the  University  of  Utah  is  on  Silver  Lake 
(altitude  8 7 28  ft.)  some  twenty  miles  from  the  Great 
Salt  Lake.  Six  small  nearby  mountain  lakes  all  have 
an  altitude  of  more  than  9000  feet. 

Doubtless,  with  the  growing  interest  in  limnological 
work,  other  lakeside  stations  will  be  added  to  this  list. 

Depth  and  Breadth — The  depth  of  lakes  is  of  more 
biological  significance  than  the  form  of  their  basins; 
for,  as  we  have  seen  in  the  preceding  chapter,  with 
increase  of  depth  goes  increased  pressure,  diminished 
light,  and  thermal  stratification  of  the  water.  Living 
conditions  are  therefore  very  different  in  shallow  water 
from  what  they  are  in  the  bottom  of  a  deep  lake,  where 
there  is  no  light,  and  where  the  temperature  remains 
constant  throughout  the  year.  Absence  of  light  pre- 
vents the  growth  of  chlorophyl -bearing  organisms  and 
renders  such  waters  relatively  barren.  The  lighted  top 
layer  of  the  water  (zone  of  photosynthesis)  is  the  pro- 
ductive area.  The  other  is  a  reservoir,  tending  to 
stabilize  conditions.     Lakes  may  therefore  be  roughly 


j2  Types  of  Aquatic  Environment 

grouped  in  two  classes:  first,  those  that  are  shallow 
enough  f<  >r  o  ariplete  circulation  of  their  water  by  wind 
or  otherwise  at  any  time ;  and  second  those  deep  enough 
to  maintain  through  a  part  of  the  summer  season  a 
bott<  >m  reserve  At  of  still  water,  undisturbed  by  waves  or 
currents,  and  stratified  according  to  temperature  and 
consequent  density.  In  these  deeper  lakes  a  thermo- 
eline  appears  during  midsummer.  In  the  lakes  of  New 
York  its  upper  limit  is  usually  reached  at  about  thirty- 
five  feet  and  it  has  an  average  thickness  of  some  fifteen 
feet.  Our  lakes  of  the  second  class  may  therefore  be 
said  to  have  a  depth  greater  than  fifty  feet. 

Lakes  of  this  class  may  differ  much  among  them- 
selves according  to  the  relative  volume  of  this  bottom 
reservoir  of  quiet  water,  Lakes  Otisco  and  Skaneateles 
(see  map  on  page  65)  serve  well  for  comparison  in  this 
regard,  since  they  are  similar  in  form  and  situation  and 
occupy  parallel  basins  but  a  few  miles  apart. 

Max.     %  of  vol. 
Area  in      depth      below        Trans-  Free  COat  at  Oxygenf  at 

Lake  sq.  mi.      in  ft.         50  ft.      parency*      surface     bottom         surface   bottom 

Otisco 2.64       66        7.0       9.2     —2.50+3.80      6.72      0.00 

Skaneateles.  13.90     297      70.2     31.8     —1.25 +1.00      6.75      7.89 

*In  feet,  measured  by  Secchi's  disc. 

fin  cc.  per  liter  of  water.  Alkalinity  by  phenolthalein  test  is  indicated 
by  the  minus  sign. 

The  figures  given  are  from  midsummer  measure- 
ments by  Birge  and  Juday.  At  the  time  these  observa- 
tions were  made  both  lakes  were  alkaline  at  the  surface, 
tho  still  charged  with  free  carbon  dioxide  at  the  bottom. 
Apparently,  the  greater  the  body  of  deep  water  the 
greater  the  reserve  of  oxygen  taken  up  at  the  time  of 
the  spring  circulation  and  held  through  the  summer 
season.  Deep  lakes  are  as  a  rule  less  productive  of 
plancton  in  summer,  even  in  their  surface  waters, 
because  their  supply  of  available  carbon  dioxide  runs 
low.     It  is  consumed  by  algae  and  carried  to  the  bottom 


Currents  73 


with  them  when  they  die,  and  thus  removed  from  cir- 
culation. 

Increasing  breadth  of  surface  means  increasing 
exposure  to  winds  with  better  aeration,  especially 
where  waves  break  in  foam  and  spray,  and  with  the 
development  of  superficial  currents.  Currents  in  lakes 
are  not  controlled  by  wind  alone,  but  are  influenced  as 
well  by  contours  of  basins,  by  outflow,  and  by  the 
centrifugal  pull  due  to  the  rotation  of  the  earth  on  its 
axis.  In  Lake  Superior  a  current  parallels  the  shore, 
moving  in  a  direction  opposite  to  that  of  the  hands  of  a 
clock.  Only  in  the  largest  lakes  are  tides  perceptible, 
but  there  are  other  fluctuations  of  level  that  are  due  to 
inequalities  of  barometric  pressure  over  the  surface. 
These  are  called  seiches. 

Broad  lakes  are  well  defined,  for  they  build  their 
own  barrier  reefs  across  every  low  spot  in  the  shores, 
and  round  out  their  outlines.  It  is  only  shores  that  are 
not  swept  by  heavy  waves  that  merge  insensibly  into 
marshes.  In  winter  in  our  latitude  the  margins  of  the 
larger  lakes  become  icebound,  and  the  shoreline  is 
temporarily  shifted  into  deeper  water  (compare  summer 
and  winter  conditions  at  the  head  of  Cayuga  lake  as 
shown  in  our  frontispiece) . 

Increasing  breadth  has  little  effect  on  the  life  of  the 
open  water,  and  none,  directly,  on  the  inhabitants  of 
the  depths;  but  it  profoundly  affects  the  life  of  the 
shoals  and  the  margins,  where  the  waves  beat,  and  the 
loose  sands  scour  and  the  ice  floes  grind.  Such  a  beach 
as  that  shown  on  page  61  is  bare  of  vegetation  only 
because  it  is  storm  swept.  The  higher  plants  cannot 
withstand  the  pounding  of  the  waves  and  the  grinding 
of  the  ice  on  such  a  shore. 

The  shallower  a  lake  is  the  better  its  waters  are 
exposed  to  light  and  air,  and,  other  things  being  equal, 
the  richer  its  production  of  organic  life. 


74 


Types  of  Aquatic  Environment 


High  and  low  water— Since  the  source  of  this  water  is 
in  the  cl<  >uds,  all  lakes  fluctuate  more  or  less  with  varia- 
tion in  rainfall.  The  great  lakes  drain  an  empire  of 
2>7.(>X8  square  miles,  about  a  third  of  which  is  covered 
by  their  waters.  They  constitute  the  greatest  system 
of  fresh  water  reservoirs  in  the  world,  with  an 
unparalleled  uniformity  of  level  and  regularity  of 
outflow.     Yet  their  depth  varies  from  month  to  month 


_                        1 

ILEVATH'N 

:hv 

mi 

1898 

1899 

{'»'(• 

1901 

1903 

tiK>3 

1SH>4 

1905 

190<i 

190  T 

INFEET 

ABOVE 

MEAN 

SEA  LEVEL 

IN  FRET 

ABOVt 

MEAN 

SEA  LEVEL 

pssi 

l.X  +  7. 

•:  ■<  i  o 

H  <  9 c 

■  >*•> 

■  <  so 

HOC 

B§5c 

kff<K 

«  y  e  » 

KX<7. 

u  1?  o 

—    2490 

^-     24A.0 

■ 

1 

f  ^ 

~      2470 

24"0      f 

\ 

j 

r  1. 

=      2460 

f\ 

A 

ft 

ft 

A 

( 

J 

L 

L 

J 

r\ 

A 

J  i 

J 

\ 

i  \ 

J    1 

"      24S.O 

I 

( 

1           U 

4 

r   \\ 

I 

t  K 

I 

7_ 

X 

I 

j 

i-    2440 

\ 

L 

= 

=      243© 

MONTHLY  MEAN  LEVEL  OF  LAKE  ONTARIO  AT  OSWEG0.N  Y 

Fig.  19.     Diagram  of  monthly  water  levels  in  Lake  Ontario  for  twelve  years, 
from  the  Report  of  the  International  Waterways  Commission  for    1910. 


and  from  year  to  year,  as  shown  on  the  accompanying 
diagram.  From  this  condition  of  relative  stability  to 
that  of  regular  disappearance,  as  of  the  strand  lakes  of 
the  Southwest,  there  are  all  gradations.  Topography 
determines  where  a  lake  may  occur,  but  climate  has 
much  to  do  with  its  continuance.  Lakes  in  arid  regions 
often  do  not  overflow  their  basins.  Continuous  evapora- 
tion under  cloudless  skies  further  aided  by  high  winds, 
quickly  removes  the  excess  of  the  floods  that  run  into 
them  from  surrounding  mountains.  The  minerals  dis- 
solved in  these  waters  are  thus  concentrated,  and  they 
becomi  •  r.lkaline  or  salt.     We  shall  have  little  to  say  in 


High  and  Low  Water 


75 


this  book  about  such  lakes,  or  about  their  population, 
but  they  constitute  an  interesting  class.  Life  in  their 
waters  must  meet  conditions  physiologically  so  different 
that  few  organisms  can  live  in  both  fresh  and  salt  water. 
Large  lakes  in  arid  regions  are  continually  salt; 
permanent  lakesof  smaller  volume  arc  made  temporarily 
fresh  or  brackish  by  heavy  inflowing  floods;     while 


Fig.  20.  Marl  pond  near  Cortland,  N.  Y.,  at  low  water.  The  whiteness  oif  the 
bed  surrounding  the  residual  pool  is  due  to  deposited  marl,  largely  derived 
from  decomposed  snail  shells.  The  marl  is  thinly  overgrown  with  small 
freely-blooming  plants  of  Polygonum  amphibitim.  Tall  aquatics  mark  the 
vernal  shore  line.     (Photo  by  H.  H.  Knight). 

strand  lakes  (called  by  the  Spanish  name  play  a  lakes, 
in  the  Southwest)  run  the  whole  gamut  of  water  con- 
tent, and  vanish  utterly  between  seasons  of  rain. 

Complete  withdrawal  of  the  waters  is  of  course  fatal 
to  all  aquatic  organisms,  save  a  few  that  have  specialized 
means  of  resistance  to  the  drought.     Partial  withdrawal 


76 


Types  of  Aquatic  Environment 


by  evaporation  means  concentration  of  solids  in  solu- 
tion, and  crowding  of  organisms,  with  limitation  of 
their  food  and  shelter.  The  shoreward  population  of 
all  lakes  is  subject  to  a  succession  of  such  vicissitudes. 
The  term  limnology  is  often  used  in  a  restricted  sense 
as  applying  only  to  the  study  of  freshwater  lakes. 
Tli is  is  due  to  the  profound  influence  of  the  Swiss 
Master,  F.  A.  Forel,  who  is  often  called  the  "Father 
of  Limnology."  He  was  the  first  to  study  lakes 
intrusively  after  modern  methods.  He  made  the 
Swiss  lakes  the  best  known  of  any  in  the  world. 
His  greatest  work  "  Le  Leman"  a  monograph  on 
Lake  Geneva,  is  a  masterpiece  of  limnological  litera- 
ture. It  was  he  who  first  developed  a  comprehen- 
sive plan  for  the  study  of  the  life  of  lakes  and  all 
its  environing  conditions. 


STREAMS 


OURNEYING  seaward, 
the  water  that  finds 
no  basins  to  retain  it, 
forms  streams.  Ac- 
cording as  these  differ 
in  size  we  call  them 
rivers,  creeks,  brooks, 
and  rills.  These  dif- 
fer as  do  lakes  in  the 
dissolved  contents  of  their  waters,  according  to  the 
nature  of  the  soils  they  drain.  Streams  differ  most 
from  the  lakes  in  that  their  waters  are  ever  moving  in 
one  direction,  and  ever  carrying  more  or  less  of  a  load 
of  silt.  From  the  geologist's  point  of  view  the  work  of 
rivers  is  the  transportation  of  the  substance  of  the 
uplands  into  the  seas.  It  is  an  eternal  levelling  process. 
It  is  well  advanced  toward  completion  in  the  broad 
flood  plains  of  the  larger  continental  streams  (see  map 
on  page  63);  but  only  well  begun  where  brooks  and 
rills  are  invading  the  high  hills,  where  the  waters  seek 
outlets  in  all  directions,  and  where  every  slope  is 
intersected  with  a  maze  of  channels.  The  rapidity  of 
the  grading  work  depends  chiefly  upon  climate  and  rain- 
fall, on  topography  and  altitude  and  on  the  character 
of  the  rocks  and  soil. 


78 


Types  of  Aquatic  Environment 


The  rivers  of  America  have  been  extensively  studied 
as  t<  i  their  hydrography,  their  navigability,  their  water- 
power  resources,  and  their  liability  to  overflow  with 
consequent  flood  damage ;   but  it  is  the  conditions  they 


Fig.    21.     Streams   of   the   upper   Cayuga   basin. 


A.  Taughannock  Creek,  with  a  waterfall  21  r  feet  high  near  its  mouth; 
B.  Salmon  Creek;  C.  Fall  Creek  with  the  Cornell  University  Biological  Field 
Station  in  the  marsh  at  its  mouth  (views  on  this  stream  are  shown  in  the  initial 
cuts  on  pages  2  4  and  82) ;  D.  Cascadilla  Creek  (view  on  page  55) ;  E.  Sixmile 
Creek;  F.  Buttermilk  Creek  with  Coys  Glen  opposite  its  mouth.  (View  on 
page  77 ;  of  the  Glen  on  page  25) ;  G.  Neguena  Creek  or  the  Inlet.  The  southern- 
most of  these  streams  rise  in  cold  swamps,  which  drain  southward  also  into 
tributaries  of  the  Susquehanna  River. 


Conditions  in  Streams 


79 


afford  to  their  plant  and  animal  inhabitants  that 
interest  us  here;  and  these  have  been  little  studied. 
Most  has  been  done  on  the  Illinois  River,  at  the  floating 
laboratory  of  the  Illinois  State  Laboratory  of  Natural 
History  (see  page  50).  A  more  recently  established 
river  laboratory,  more  limited  in  its  scope  (being 
primarily  concerned  with  the  propagation  of  river 
mussels)  is  that  of  the  U.  S.  Fish  Commission  at  Fair- 
port,  Iowa,  on  the  Mis- 
sissippi River. 

In  large  streams,  espec- 
ially in  their  deeper  and 
more  quiet  portions,  the 
conditions  of  life  are  most 
like  those  in  lakes.  In  les- 
ser streams  life  is  subject 
to  far  greater  vicissitudes. 
The  accompanying  figure 
shows  comparative  sum- 
mer and  winter  tempera- 
tures in  air  and  in  water  of 
Fall  Creek  at  Ithaca.  This 
creek  (see  the  figure  on 
page  24),  being  much 
broken  by  waterfalls  and 
very  shallow,  shows  hardly 
any  difference  between  sur- 
face and  bottom  tempera- 
tures. The  summer  tem- 
peratures of  air  and  water 
(fig.  22)  are  seen  to  main- 
tain a  sort  of  correspond- 
ence, in  spite  of  the  thermal 
conservatism  of  water,  due  to  its  greater  specific  heat. 
This  approximation  is  due  to  conditions  in  the  creek 
which  make  for  rapid  heating  or  cooling  of  the  water. 


Fig.  22.  Diagram  showing  summer 
and  winter  conditions  in  Fall  Creek 
at  Ithaca,  N.  Y.  Data  on  air 
temperatures  furnished  by  Dr.  W.M. 
Wilson  of  the  U.  S.  Weather  Bureau. 
Data  on  water  temperatures  by  Pro- 
fessor E.  M.  Chamot. 


So  Types  of  Aquatic  Environment 

It  flows  in  thin  sheets  over  broad  ledges  of  dark  colored 
r<  h  ks  that  are  exposed  to  the  sun,  and  it  falls  over  pro- 
jecting  ledges  in  br<  >ad  thin  curtains,  outspread  in  con- 
tact with  the  air. 

The  curves  for  the  two  winter  months,  show  less 
concurrence,  and  it  is  strikingly  apparent  that  during 
that  period  when  the  creek  was  ice-bound  (Dec.  15- 
Jan.  31)  the  water  temperature  showed  no  relation  to 
air  temperature,  but  remained  constantly  at  or  very 
close  too°C.  (320  F.). 

Forbes  and  Richardson  (13)  have  shown  how  great 
may  be  the  aerating  effect  of  a  single  waterfall  in  such 
a  sewage  polluted  stream  as  the  upper  Illinois  River. 
"The  fall  over  the  Marseilles  dam  (710  feet  long  and  10 
feet  high)  in  the  hot  weather  and  low  water  period  of 
July  and  August,  191 1,  has  the  effect  to  increase  the 
dissolved  oxygen  more  than  four  and  a  half  times,  rais- 
ing it  from  an  average  of  .64  parts  per  million  to  2.94 
parts.  On  the  other  hand,  with  the  cold  weather,  high 
oxygen  ratios,  and  higher  water  levels  of  February  and 
March,  1 91 2,  and  the  consequent  reduced  fall  of 
water  at  Marseilles,  the  oxygen  increase  was  only  18 
per  cent. — from  7.35  parts  per  million  above  the  dam 
to  8.65  parts  below  *  *  *  The  beneficial  effect  is 
greatest  when  it  is  most  needed — when  the  pollution  is 
most  concentrated  and  when  decomposition  processes 
are  most  active." 

Ice — The  physical  conditions  that  in  temperate 
regions  have  most  to  do  with  the  well-  or  ill-being  of 
organisms  living  in  running  water  are  those  resulting 
from  the  freezing.  The  hardships  of  winter  may  be 
very  severe,  especially  in  shallow  streams.  One  may 
stand  beside  Fall  Creek  in  early  wTinter  when  the  thin 
ice  cakes  heaped  with  snow  are  first  cast  forth  on  the 
stream,  and  see  through  the  limpid  water  an  abundant 


Ice  in  Streams  81 


life  gathered  upon  the  stone  ledges,  above  which  these 
miniature  floes  are  harmlessly  drifting.  There  are 
great  black  patches  of  Simidium  larvae,  contrasting 
strongly  with  the  whiteness  of  the  snow.  There  are 
beautiful  green  drapings  of  Cladophora  and  rich  red- 
purple  fringes  of  Chantransia,  and  everywhere  amber- 
brown  carpet ings  of  diatoms,  overspreading  all  the 
bottom.  But  if  one  stand  in  the  same  spot  in  the 
spring,  after  the  heavy  ice  of  winter  has  gone  out,  he 
will  see  that  the  rocks  have  been  swept  clean  and  bare, 
every  living  thing  that  the  ice  could  reach  having  gone. 

The  grinding  power  of  heavy  ice,  and  its  pushing 
power  when  driven  by  waves  or  currents,  are  too  well 
known  to  need  any  comment.  The  effects  may  be  seen 
on  any  beach  in  spring,  or  by  any  large  stream.  But 
there  is  in  brooks  and  turbulent  streams  a  cutting  with 
fine  ice  rubble  that  works  through  longer  periods,  and 
adds  the  finishing  touches  of  destructives ss.  It  is 
driven  by  the  water  currents  like  sand  in  a  blast,  and  it 
cleans  out  the  little  crevices  that  the  heavy  ice  could 
not  enter.  This  ice  rubble  is  formed  at  the  front  of 
water  falls  under  such  conditions  as  are  shown  in  the 
accompanying  figure  of  Triphammer  Falls  at  Ithaca. 
The  pool  below  the  fall  froze  first.  The  winter  increas- 
ing cold,  the  spray  began  to  freeze  where  it  fell.  It 
formed  icicles,  large  and  small,  wherever  it  could  find  a 
support  above.  It  built  up  grotesque  columns  on  the 
edge  of  the  ice  of  the  pool  beneath.  It  grew  inward 
from  the  sides  and  began  to  overarch  the  stream  face; 
and  then,  with  favoring  intense  cold  of  some  days  dura- 
tion, it  extended  these  lines  of  frozen  spray  across  the 
front  of  the  fall  in  all  directions,  covering  it  as  with  a 
beautiful  veil  of  ice. 

The  conditions  shown  in  the  picture  are  perfect  for 
the  rapid  formation  of  ice  rubble.  From  thousands  of 
points  on  the  underside  of  this  tesselated  structure 


82 


Types  of  Aquatic  Environment 


minute  icicles  are  forming  and  their  tips  are  being  broken 
►y  the  oscillations  of  the  current.  These  broken 
tips  constitute 
the  rubble. 
They  are  some- 
times remark- 
ably uniform  in 
size— thoseform- 
ing  when  this 
picture  w a  s 
t  a  k  en  were 
ab<  >ut  the  size 
of  peas — and 
though  small 
they  are  the 
t<><»ls  with  which 
the  current  does 
its  winter  clean- 
ing. In  the 
ponds  formed  by 
damming  rapid 
streams  this  rub- 
ble accumulates 
under  the  solid 
ice. 

"Anchor  ice,, 
forms  in  the 
beds  of  rapid 
streams,  and 
adds  another 
peril  to  their  in- 
habitants. The 
water,  cooled     „  _.    .  _  .  ,  „  „    «      „ 

.     .           V       r  Fir,.  23.     The  ice  veil  on  Triphammer  Falls,  Cornell 

DelOW  the  treez-  University  Campus.     The  fall  is  at  the  left,  the 

in°"  point  bv  COn-  Laboratory  of  Hydraulic  Engineering  at  the  right 

..."         .  in  the  picture,  the  onlv  open  water  seen  is  in  the 

tact  With  the  air,  foaming  pool  at  the  foot  of  the  fall. 


Anchor  Ice 


»3 


does  not  freeze  in  the  current  because  of  its  motion, 
but  it  does  freeze  on  the  bottom  where  the  current 
is  sufficiently  retarded  to  allow  it.  It  congeals  in 
semi-solid  or  more  or  less  flocculent  masses  which,  when 
attached  to  the  stones  of  the  bed,  often  buoy  them  up 


Fig. 


14.     A  brook  in  winter.     Country  Club  woods,  Ithaca,  N.  Y 

Photo  by  John  T.  Xeedham. 


Thus  the  organ- 


and  cause  them  to  be  carried  away. 

isms  that  dwell  in  the  stream  bed  are  deprived  of  their 

shelter  and  exposed  to  new  perils. 

Below  the  frost-line,  however,  in  streams  where 
dangers  of  mechanical  injuries  such  as  above  men- 
tioned are  absent,  milder  moods  prevail.  In  the  bed 
of  a  gentle  meandering  streamlet  like  that  shown  in  the 
accompanying  figure,  life  doubtless  runs  on  in  winter 


v_^  Types  of  Aquatic  Environment 

with  greater  serenity  than  on  land.  Diatoms  grow 
and  caddis-worms  forage  and  community  life  is  actively 
maintained. 

Silt — Part  of  the  substance  of  the  land  is  carried 
seaward  in  solution.  It  is  ordinarily  dissolved  at  or 
near  the  surface  of  the  ground,  but  may  be  dissolved 
from  underlying  strata,  as  in  the  region  of  the  Mam- 
moth Cave  in  Kentucky,  where  great  streams  run  far 
under  ground.  But  the  greater  part  is  carried  in 
suspension.  Materials  thus  carried  vary  in  size  from 
the  finest  particles  of  clay  to  great  trees  dropped  whole 
into  the  stream  by  an  undercutting  flood.  The  lighter 
solids  float,  and  are  apt  to  be  heaped  on  shore  by  wave 
and  wind.  The  heavier  are  carried  and  rolled  along, 
more  or  less  intermittently,  hastened  with  floods  and 
slackened  with  low  water,  but  ever  reaching  lower 
levels.  The  rate  of  their  settling  in  relation  to  size 
and  to  velocity  of  stream  has  been  discussed  in  the 
preceding  chapter. 

Silt  is  most  abundant  at  flood  because  of  the  greater 
velocity  of  the  water  at  such  times.  Kofoid  ('03)  has 
studied  the  amount  of  silt  carried  by  the  Illinois  River 
at  Havana.  Observations  at  one  of  his  stations 
extending  over  an  entire  year  show  a  minimum  amount 
of  140  cc.  per  cubic  meter  of  river  water;  a  maximum 
of  4,284  cc,  and  an  average  for  the  year  (28  samples) 
of  1 .572  cc.  Silt  in  a  stream  affects  its  population  in  a 
number  of  ways.  It  excludes  light  and  so  interferes 
with  the  growth  of  green  plants,  and  thus  indirectly  with 
the  food  supply  of  animals.  It  interferes  with  the  free 
locomotion  of  the  microscopic  animals  by  becoming 
entangled  in  their  swimming  appendages.  It  clogs  the 
respiratory  apparatus  of  other  animals.  It  falls  in 
dejx  >sits  that  smother  and  bury  both  plants  and  animals 
living  on  the  bottom.  Thus  the  best  foraging  grounds 
of  some  of  our  valuable  fishes  are  ruined. 


Current  85 


Professor  Forbes  ('00)  has  shown  that  the  fine  silt 
from  the  earlier-glaciated  and  better  weathered  soils 
of  southern  Illinois,  has  been  a  probable  cause  of 
exclusion  of  a  number  of  regional  fishes  from  the  streams 
of  that  portion  of  the  state. 

It  is  heavier  silt  that  takes  the  larger  share  in  the 
building  of  bars  and  embankments  along  the  lower 
reaches  of  a  great  stream,  in  raising  natural  levees  to 
hold  impounded  backwaters,  and  in  blocking  cut-off 
channels  to  make  lakes  of  them. 

Current — Rate  of  streamflow  being  determined 
largely  by  the  gradient  of  the  channel,  is  one  of  the 
more  constant  features  of  rivers,  but  even  this  is  sub- 
ject to  considerable  fluctuation  according  to  volume. 
Kofoid  states  that  water  in  the  Illinois  River  travels 
from  Utica  to  the  mouth  (227  miles)  in  five  days  at 
flood,  but  requires  twenty -three  days  for  the  journey 
at  lowest  water.  The  increase  in  speed  and  in  turbu- 
lence in  flood  time  appears  to  have  a  deleterious  effect 
upon  some  of  the  population,  many  dead  or  moribund 
individuals  of  free  swimming  entomostraca  being 
present  in  the  waters  at  such  times. 

With  the  runoff  after  abundant  rainfall  a  rapid  rise 
and  acceleration  occurs,  to  be  followed  by  a  much 
slower  decline.  The  stuffs  in  the  water  are  diluted; 
the  plancton  is  scattered.  A  new  load  of  silt  is  received 
from  the  land;  plant  growths  are  destroyed  and  even 
contours  in  the  channel  are  shifted. 

Current  is  promoted  by  increasing  gradient  of  stream  • 
bed.  It  is  diminished  by  obstructions,  such  as  rocks  or 
plant  growths,  by  sharp  bends,  etc.  It  is  slightly 
accelerated  or  retarded  by  wind  according  as  the  direc- 
tion is  up  or  down  stream.  Even  where  a  stream 
appears  to  be  flowing  steadily  over  an  even  bed  between 
smooth  shores,  careful  measurements  reveal  slight  and 


Types  of  Aquatic  Environment 


Depth 

Feet 

in   inches 

per  sec. 

2 

3-91 

3 

373 

4 

3.60 

5 

3-32 

6 

304 

: 

2.89 

8 

2.81 

id 

2-73 

12 

2.64 

M 

2.46 

15 

2.17 

1 6 

i-73 

inconstant  fluctuations.  The  current  is  nowhere  uni- 
f(  >rm  from  top  to  bottom  or  from  bank  to  bank.  In  the 
horizontal  plane  it  is  swiftest  in  midstream  and  is 
retarded  by  the  banks.  In  a  vertical  plane,  it  is  swift- 
est just  beneath  the  surface  and  is  retarded  more  and 
•  t<  ward  the  bottom.     The  pull  of  the  surface  him 

retards  it  a  little  and 
when  ice  forms  on  the 
surface,  friction  against 
the  ice  retards  it  far  more 
and  throws  the  point  of 
maximum  velocity  down 
near  middepth  of  the 
stream.  A  sample  meas- 
urement made  by  Mr. 
Wilbert  A.  Clemens  in 
Cascadilla  Creek  at 

and     Depth     in     Cascadilla    Ithaca       in      Open      Water 
Creek.    Measured  by  W.  A.  Clemens,    seventeen       inches       deep 

gave  rate  of  flow  varying  from  a  maximum  of  3 . 9 1  feet  per 
second  two  inches  below  the  surface  down  to  1 .  73  feet  per 
second  one  inch  above  the  bottom,  as  shown  in  the  col- 
umns above.  Below  this,  in  the  last  inch  of  depth  the 
retardation  was  more  rapid,  but  irregular.  The  current 
slackens  more  slowly  toward  the  surface  and  toward 
the  side  margins  of  the  stream. 

Mr.  Clemens,  using  a  small  Pitot-tube  current  meter, 
made  other  measurements  showing  that  in  the  places 
where  dwell  the  majority  of  the  inhabitants  of  swift 
streams  there  is  much  less  current  than  one  might  ex- 
pect. In  the  shelter  of  stones  and  other  obstructions 
there  is  slack  water.  On  sloping  bare  rock  bottoms 
under  a  swiftly  gliding  stream  the  current  is  often  but 
half  that  at  the  surface.  On  stones  exposed  to  the 
current  a  coating  of  slime  and  diatomaceous  ooze 
reduces  the  current  16  to  32  per  cent. 


High  and  Low 


Water 


87 


This  accounts  for  the  continual  restocking  of  a  stream 
whose  waters  are  swifter  than  the  swimming  of  the 
animals  found  in  the  open  channels.  In  these  more  or 
less  shoreward  places  they  breed  and  renew  the  supply. 
Except  in  a  stream  whose  waters  run  a  long  course  sea- 
ward, allowing  an  ample  time  for  breeding,  there  is 
little  indigenous  free-swimming  population. 


Fig.  25.  Annually  inundated  bulrush-covered  flood-plain  at  the  mouth  of  Fall 
Creek,  Ithaca,  N.  Y.,  in  1908.  Clear  growth  of  Scirpus  fluviatilis  and  a 
drowned  elm  tree.  The  Cornell  University  Biological  Field  Station  at 
extreme  right.     West  Hill  in  the  distance. 


High  and  Low  Water — Inconstancy  is  a  leading  char- 
acteristic of  river  environment,  and  this  has  its  chief 
cause  in  the  bestowal  of  the  rain.  Streams  fed  mainly 
by  springs,  lakes,  and  reservoirs  are  relatively  constant; 
but  nearly  all  water  courses  are  subject  to  overflow; 
their  channels  are  not  large  enough  to  carry  flood 
waters,  so  these  overspread  the  adjacent  bottomlands. 
Every  change  of  level  modifies  the  environment  by 


Types  of  Aquatic  Environment 

connecting  or  cutting  off  back  waters,  by  shifting  cur- 
rents, by  disturbing  the  adjustment  of  the  vegetation, 
and  by  causing  the  migration  of  the  larger  animals.  At 
1<  >w  water  the  Illinois  River  above  Havana  has  a  width 
of  some  500  feet;  in  flood  times  it  spreads  across  the 
valley  floor  in  an  unbroken  sheet  of  water  four  miles 
wide.  Kofoid  estimates  that  at  time  of  high  flood  (18 
feet  above  low-water  datum)  less  than  one-tenth  as 
much  of  this  water  is  in  the  channel  as  lies  beyond  its 
boundaries. 

The  rise  of  a  river  flood  is  often  sudden;  the  decline 
is  always  much  more  gradual,  for  impounding  barriers 
and  impeding  vegetation  tend  to  hold  the  water  upon 
the  lowlands.  The  period  of  inundation  markedlv 
affects  the  life  of  the  land  overflowed.  Cycles  of  seasons 
with  short  periods  of  annual  submergence  favor  the 
establishment  of  upland  plants  and  trees.  Cycles  of 
years  of  more  abundant  rainfall  favor  the  growth  of 
swamp  vegetation.  Certain  plants  like  the  flood-plain 
bulrush  shown  in  the  preceding  figure  seem  to  thrive 
best  under  inconstancv  of  flood  conditions. 


MARSHES,   SWAMPS   AND   BOGS 


GREAT  aquatic  en- 
vironment may  be 
maintained  with 
much  less  water  than  there  is  in  a  lake  or  a  river  if  only 
an  area  of  low  gradient,  lacking  proper  basin  or  channel, 
be  furnished  with  a  ground  cover  of  plants  suitable  for 
retaining  the  water  on  the  soil.  Enough  water  must  be 
retained  to  prevent  the  complete  decay  of  the  accumu- 
lating plant  remains.  Then  we  will  have,  according  to 
circumstances,  a  marsh,  a  swamp  or  a  bog. 

There  are  no  hard  and  fast  distinctions  between  these 
three;  but  in  general  we  may  speak  of  a  marsh  as 
a  meadow-like  area  overgrown  with  herbaceous  aquatic 
plants,  such  as  cat-tail,  rushes  and  sedges;  of  a  swamp 
as  a  wet  area  overgrown  with  trees ;  and  of  a  bog  as  such 
an  area  overgrown  with  sphagnum  or  bog-moss,  and 
yielding  under  foot.  The  great  Montezuma  Marsh  of 
Central   New  York    (shown  in  the  initial  above)    is 

89 


90  Types  of  Aquatic  Environment 


typical  of  the  first  class;  the  Dismal  Swamp  of  eastern 
Virginia,  of  the  second;  and  over  the  northern  lake 
region  of  the  continent  there  are  innumerable  examples 
of  the  third.  These  types  are  rarely  entirely  isolated, 
h<  wever,  since  both  marsh  and  bog  tend  to  be  invaded 
by  tree  gr<  >wth  at  their  margins.  Such  wet  lands  occupy 
a  superficial  area  larger  by  far  than  that  covered  by 
lakes  and  rivers  of  every  sort.  They  cover  in  all 
probably  more  than  a  hundred  million  acres  in  the 
United  States;  great  swamp  areas  border  the  Gulf 
of  Mexico,  the  South  Atlantic  seaboard,  and  the  lower 
reaches  of  the  Mississippi,  and  of  its  larger  tributaries, 
and  partially  overspread  the  lake  regions  of  upper 
Minnesota,  Wisconsin,  Michigan  and  Maine.  In  the 
order  of  the  areas  of  ''swamp  land"  (officially  so  desig- 
nated)  within  their  borders  the  leading  states  are 
Florida,  Louisiana,  Arkansas,  Mississippi,  Michigan, 
Minnesota,  Wisconsin  and  Maine. 

Swamps  naturally  occupy  the  shoal  areas  along  the 
shores  of  lakes  and  seas.  Marine  swamps  below  mean 
tide  occur  as  shoals  covered  with  pliant  eel-grass. 
Above  mean  tide  they  are  meadow-like  areas  located 
behind  protecting  barrier  reefs,  or  they  are  mangrove 
thickets  that  fringe  the  shore  line,  boldly  confronting 
the  waves.  With  these  we  are  not  here  concerned. 
Fresh -water  marshes  likewise  occupy  the  shoals  border- 
ing the  larger  lakes,  where  protected  from  the  wTaves  by 
the  bars  that  mark  the  shore  line.  In  smaller  lakes, 
where  not  stopped  by  wave  action,  they  slowly  invade 
the  shoaler  waters,  advancing  with  the  filling  of  the 
basin,  and  themselves  aiding  in  the  filling  process. 

That  erosion  sometimes  gives  rise  to  lakes  has 
already  been  pointed  out;  much  oftener  it  produces 
marshes;  for  depositions  of  silt  in  the  low  reaches  of 
streams  are  much  more  likely  to  produce  shoals  than 
deep  water. 


Cat-Tail  Marshes 


9i 


Cat-tail  Marshes — In  the  region  of  great  lakes  every 
open  area  of  water  up  to  ten  feet  in  depth  is  likely  to 
be  invaded  by  the  cat-tail  flag  {Typha).  The  ready 
dispersal  of  the  seeds  by  winds  scatters  the  species 
everywhere,  and  no  permanent  wet  spot  on  the  remotest 
hill-top  is  too  small  to  have  at  least  a  few  plants.     Along 


Fig.  26.  An  open-water  area  (Parker's  Pond)  in  the  Montezuma  Marsh  in 
Central  New  York.  Formerly  it  teemed  with  wild  water  fowl.  It  is  sur- 
rounded by  miles  of  cat- tail  flags  (Typha)  of  the  densest  sort  of  growth. 

the  shores  of  the  Great  Lakes  and  in  the  broad  shoals 
bordering  on  the  Seneca  River  there  are  meadow-like 
expanses  of  Typha  stretching  away  as  far  as  the  eye 
can  see.  Many  other  plants  are  there  also,  as  will  be 
noted  in  a  subsequent  chapter,  but  Typha  is  the 
dominant  plant,  and  the  one  that  occupies  the  fore- 
front of  the  advancing  shore  vegetation.  It  masses  its 
crowns  and  numberless  interlaced  roots  at  the  surface 


9^ 


Types  of  Agnatic  Environment 


of  the  water  in  floating  rafts,  which  steadily  extend  into 
deeper  water.  The  pond  in  the  center  of  Montezuma 
Marsh  shown  in  the  preceding  figure  is  completely 
surrounded  by  a  rapidly  advancing,  half-floating  even- 
fronted  phalanx  of  cat-tail. 


>*■ 


■■ 


Fi<;.  27.  ''The  Cove"  at  the  Cornell  University  Biological  Field  Station,  in 
time  of  high  water.  Early  summer.  Two  of  the  University  buildings 
appear  on  the  hill  in  the  distance. 


Later  conditions  in  such  a  marsh  are  those  illustrated 
by  our  frontispiece :  regularly  alternating  spring  floods, 
summer  luxuriance,  autumn  burning  and  winter  freez- 
ing. This  goes  on  long  after  the  work  of  the  cat-tail, 
the  pioneer  landbuilding,  has  been  accomplished. 
The  excellent  aquatic  collecting  ground  shown  in  the 
accompanying  figure  is  kept  open  only  by  the  annual 
removal  of  the  encroaching  flag. 


Okefenokee  Swamp 


93 


The  Okefenokee  Swamp.  In  southern  Georgia  lies 
this  most  interesting  of  American  swamps.  It  is 
formed  behind  a  low  barrier  that  lies  in  a  N.,  N.  E. — 
S.,  S.  W.  direction  across  the  broad  sandy  coastal  plain, 
intersecting  the  course  of  the  southernmost  rivers  of 


Fig.  28.  A  view  of  "Chase's  Prairie"  in  the  more  open  eastern  portion  of  the 
Okefenokee  Swamp,  taken  from  an  elevation  of  fifty  feet  up  a  pine  tree  on 
one  of  the  incipient  islets.  The  water  is  of  uniform  depth  (about  four  or 
five  feet).     This  is  one  of  the  most  remarkable  landscapes  in  the  world. 

Photo  by  Mr.  Francis  Harper. 

Georgia  that  drain  into  the  Atlantic.  Behind  the  bar- 
rier the  waters  coming  from  the  northward  are  retained 
upon  a  low,  nearly  level  plain,  that  is  thinly  overspread 
with  sand  and  underlaid  with  clay.  They  cover  an 
area  some  forty  miles  in  diameter,  hardly  anywhere  too 
deep  for  growth  of  vascular  plants.  There  is  little  dis- 
coverable current  except  in  the  nascent  channels  of  the 


94  Types  of  Aquatic  Environment 

two  outflowing  streams,  St.  Mary's  and  Suwannee 
Rivers.  The  waters  are  deeper  over  the  eastern  part  of 
the  swamp,  the  side  next  the  barrier;  and  here  the 
station  is  mainly  herbaceous  plants,  principally 
submerged  aquatics,  with  occasional  broad  meadow- 
like areas  overgrown  with  sedges.  These  are  the  so- 
called  "prairies."  The  western  part  of  the  swamp 
(omitting  from  consideration  the  islands)  is  a  true 
swamp  in  appearance  being  covered  with  trees,  prin- 
cipally cypress.  A  few  small  strips  of  more  open  and 
deeper  water  (attaining  25  feet)  of  unique  beauty, 
owing  to  their  limpid  brown  waters  and  their  setting 
of  Tillandsia-covered  forest,  are  called  lakes. 

The  whole  swamp  is  in  reality  one  vast  bog.  Its 
waters  are  nearly  everywhere  filled  with  sphagnum. 
Whatever  appears  above  water  to  catch  the  eye  of  the 
traveler,  whether  cypress  and  tupelo  in  the  western  part 
or  sedges  and  water  lilies  on  the  "prairie,"  everywhere 
1  >eneath  and  at  the  surface  of  the  water  there  is  sphag- 
num; and  it  is  doubtless  to  the  waterholding  capacity 
of  this  moss  that  the  relative  constancy  of  this  great 
swamp  on  a  gently  inclined  plain  near  the  edge  of  the 
tropics,  is  due. 

Climbing  bogs — In-so-far  as  swamps  possess  any  basin 
at  all  they  approximate  in  character  to  shallow  lakes; 
but  there  are  extensive  bogs  in  northern  latitudes  that 
are  built  entirely  on  sloping  ground;  often  even  on 
convex  slopes.  These  are  the  so-called  "climbing 
bogs."  They  belong  to  cool -temperate  and  humid 
regions.  They  exist  by  the  power  of  certain  plants, 
notably  sphagnum,  to  hold  water  in  masses,  while 
giving  off  very  little  by  evaporation  from  the  surface. 
A  climbing  bog  proceeds  slowly  to  cover  a  slope  by  the 
growth  of  the  mass  of  living  moss  upward  against 
gravity,  and  in  time  what  was  a  barren  incline  becomes 
"  deep  spongy  mass  of  water  soaked  vegetation. 


Conditions  in  Swamps  95 

Conditions  of  life — In  the  shoal  vegetation-choked 
waters  of  marshes  there  is  little  chance  for  the  formation 
of  currents  and  little  possibility  of  disturbance  by  wind. 
Temperature  conditions  change  rapidly,  however,  owing 
to  the  heat  absorbing  and  heat  radiating  power  of  the 
black  plant-residue.  The  diurnal  range  is  very  great, 
water  that  is  cool  of  a  morning  becomes  repellantly  hot 
of  a  summer  afternoon.  Temperatures  above  900  F. 
are  not  then  uncommon.  Unpublished  observations 
made  by  Dr.  A.  A.  Allen  in  shoal  marsh  ponds  at  the 
Cornell  Biological  Field  Station  throughout  the  year 
1909,  show  a  lower  temperature  at  the  surface  of  the 
water  than  in  the  bottom  mud  from  December  to  April, 
with  reverse  conditions  for  the  remainder  of  the  year. 
The  black  mud  absorbs  and  radiates  heat  rapidly. 

Conditions  peculiar  to  marshes,  swamps  and  bogs  are 
those  due  to  massed  plant  remains  more  or  less  per- 
manently saturated  with  water.  Water  excludes  the 
air  and  hinders  decay.  Half  disintegrated  plant 
fragments  accumulate  where  they  fall,  and  continue 
for  a  longer  or  shorter  time  unchanged.  According  to 
their  state  of  decomposition  they  form  peat  or  muck. 

In  peat  the  hard  parts  and  cellular  structure  of  the 
plant  are  so  well  preserved  that  the  component  species 
may  be  recognized  on  microscopic  examination.  To 
the  naked  eye  broken  stems  and  leaves  appear  among 
the  finer  fragments,  the  whole  forming  a  springy  or 
spongy  mass  of  a  loose  texture  and  brownish  color. 
The  color  deepens  with  age,  being  lightest  immediately 
under  the  green  and  living  vegetation,  and  darkest  in 
the  lower  strata,  where  always  less  well  preserved. 

The  water  that  covers  beds  of  peat  acquires  a  brown- 
ish color  and  more  or  less  astringent  taste  due  to  in- 
fusions of  plant-stuffs.  Humous  acids  are  present  in 
abundance  and  often  solutions  of  iron  sulphate  and 
other  minerals. 


96  Types  of  Aquatic  Environment 

Muck  is  formed  by  the  more  complete  decay  of  such 
water  plants  as  compose  peat.  The  process  of  decay  is 
furthered  either  by  occasional  exposure  of  the  beds  to 
the  air  in  spells  of  drought,  or  by  the  presence  of  lime 
in  the  surrounding  soil,  correcting  the  acidity  of  the 
water  and  lessening  its  efficiency  as  a  preservative. 
Muck  is  soft  and  oozy,  paste-like  in  texture  and  black 
in  color.  In  the  openings  of  marshes,  like  that  shown 
on  page  89  are  beds  of  muck  so  soft  that  he  who  ven- 
tures to  step  on  it  may  sink  in  it  up  to  his  neck.  In 
such  a  bed  the  slow  decomposition  that  goes  on  in  hot 
weather  in  absence  of  oxygen  produces  gases  that 
gather  in  bubbles  increasing  in  size  until  they  are  able 
to  rise  and  disrupt  the  surface.*  So  are  formed  marsh 
gas  (methane)  which  occasionally  ignites  spontaneously, 
in  mysterious  flashes  over  the  water — the  well  known 
"Jack-o-lantern"  or  "Will-o-the-wisp"  or  "Ignis 
fatuus" — and  hydrogen  sulphide  which  befouls  the  sur- 
rounding atmosphere. 

The  presence  in  marsh  pools  of  these  noxious  gases, 
of  humous  acids,  and  of  bitter  salts,  and  of  the  absence 
of  oxygen — except  at  the  surface,  limits  their  animal 
population  in  the  main  to  such  creatures  as  breathe  air 
at  the  surface  or  have  specialized  means  of  meeting 
these  untoward  conditions. 

High  and  Low  Water — Swamps  being  the  shoalest  of 
waters  are  subject  to  the  most  extreme  fluctuations. 
That  they  retain  through  most  dry  seasons  enougTi 
water  for  a  permanent  aquatic  environment  is  largely 
due  to  the  water-retaining  power  of  aquatic  plants. 
Notable  among  these  is  sphagnum,  which  holds  en- 
meshed in  its  leaves  considerable  quantities  of  water, 
lifted  above  the  surrounding  water  level.     Aquatic  seed 


^ee  Penhallow,  "A  blazing  beach"  in  Science,  22:794-6,  1905. 


High  and  Low  Water  97 

plants,  also,  whose  stems  in  life  are  occupied  with 
capacious  air  spaces,  fill  with  water  when  dead  and 
fallen,  and  hold  it  by  capillarity.  So,  they  too,  form 
in  partial  decay  a  soft  spongy  water-soaked  ground 
cover. 

Marshes  develop  often  a  wonderful  density  of  popu- 
lation, for  they  have  at  times  every  advantage  of  water, 
warmth  and  light.  The  species  are  fewer,  however, 
than  in  the  more  varied  environment  of  land.  Com- 
paratively few  species  are  able  to  maintain  themselves 
permanently  where  the  pressure  for  room  is  so  great 
when  conditions  for  growth  are  favorable,  and  where 
these  conditions  fail  more  or  less  completely  every  dry 
season.  Aquatic  creatures  that  can  endure  the  condi- 
tions shown  ^^  in  the  accompanying  figure 
must  have  S^^Q  m  specialized  means  of  tiding 
over   the       ^T\V  'S&     period  of  drouth. 


r     .* 

* 

-?** 

"*r 

<*-* 

A          * 

j*«'  \ 

** 

•v 

*$$&£'%$&  * ' 

^fcu 

1 

"11                  A' 

H 

Fig.  29.     The  bed  of  a  marsh  pool  in  a  dry  season,  showing  deep  mud  crack 
and  a  thin  growth  of  bur-marigold  and  spike-rush. 


CHAPTER  IV 

AQUATIC  ORGANISMS 


IS  the  testimony  of  all 
biology  that  the  water 
was  the  original  home  of 
life  upon  the  earth. 
Conditions  of  living  are 
simpler  there  than  on 
the  land.  Food  tends 
to  be  more  uniformly  dis- 
tributed. The  perils  of 
evaporation  are  absent. 
Water  is  a  denser  medi- 
um than  air,  and  sup- 
ports the  body  better,  and  there  is,  in  the  beginning, 
less  need  of  wood  or  bone  or  shell  or  other  supporting 
structures.  Life  began  in  the  water,  and  the  simpler 
forms  of  both  plants  and  animals  are  found  there  still. 
But  not  all  aquatic  forms  have  remained  simple. 
For  when  they  multiplied  and  spread  and  filled  all  the 
waters  of  the  earth  the  struggle  for  existence  wrought 
diversification  and  specialization  among  them,  in  water 
as  on  land.  The  aquatic  population  is,  therefore,  a 
mixture  of  forms  structurally  of  high  and  low  degree. 
All  the  types  of  plant  and  animal  organization  are 
represented  in  it.  But  they  are  fitted  to  conditions  so 
different  from  those  under  which  terrestrial  beings  live 
as  to  seem  like  another  world  of  life. 


99 


100 


Aquatic  Organisms 


The  population  of  the  water  includes  besides  the 

original   inhabitants — those   tribes   that   have  always 

ived  in  the  water — a  mixture  of  forms  descended  from 

ancestors  that  once  lived  on 
land.  The  more  primitive 
groups  are  most  persistently 
aquatic.  Comparatively  few 
members  of  those  groups  that 
have  become  thoroughly  fit- 
ted for  life  on  land  have  re- 
turned to  the  water  to  live. 


WATER   PLANTS 


VERY  large  group  of  plants 
has  its  aquatic  members. 
The  algae  alone  are  predomi- 
nantly aquatic.  Most  of  them  live  wholly  immersed; 
some  live  in  moist  places,  and  a  few  in  dry  places, 
having  special  fitnesses  for  avoiding  evaporation.  In 
striking  contrast  with  this,  all  the  higher  plants,  the 
seed  plants,  ferns,  and  mosses,  center  upon  the  land, 
having  few  species  in  wet  places  and  still  fewer  wholly 
immersed.  Their  heritage  of  parts  specially  adapted 
to  life  on  land  is  of  little  value  in  the  water.  Rhi- 
zoids  as  foraging  organs,  a  thick  epidermis  with  auto- 
matic air  pores,  and  strong  supporting  tissues  are  little 
needed  under  water.  These  plants  have  all  a  shore- 
ward distribution,  and  do  not  belong  to  the  open  water. 
Only  algae,  molds  and  bacteria  are  found  in  all  waters. 


The  Algae  101 


THE  ALGAE 

It  is  a  vast  assemblage  of  plants  that  makes  up  this 
group;  and  they  are  wonderfully  diverse.  Most  of 
them  are  of  microscopic  size,  and  few  of  even  the  larger 
ones  intrude  upon  our  notice.  Notwithstanding  their 
elegance  of  form,  their  beauty  of  coloration  and  their 
great  importance  in  the  economy  of  water  life,  few  of 
them  are  well  known.  However,  certain  mass  effects 
produced  by  algae  are  more  or  less  familiar.  Massed 
together  in  inconceivably  vast  numbers  upon  the  sur- 
face of  still  water,  their  microscopic  hosts  compose  the 
' 'water  bloom. ' '  Floating  free  beneath  the  surface  they 
give  to  the  water  tints  of  emerald*  of  amberf  or  of 
blood t  Matted  masses  of  slender  green  filaments 
compose  the  growths  that  float  on  oxygen  bubbles  to 
the  surface  in  the  spring  as  "pond  scums."  Lesser 
masses  of  delicately  branched  filaments  fringe  the 
rocky  ledges  in  the  path  of  the  cataract,  or  encircle  sub- 
merged sticks  and  piling  in  still  waters.  Mixtures  of 
various  gelatinous  algae  coat  the  flat  rocks  in  clear 
streams,  making  them  green  and  slippery;  and  a  rich 
amber-tinted  layer  of  diatom  ooze  often  overspreads  the 
stream  bed  in  clear  waters. 

These  are  all  mass  effects.  To  know  the  plants  com- 
posing the  masses  one  must  seek  them  out  and  study 
them  with  the  microscope.  Among  all  the  hosts  of 
fresh  water  algae,  only  a  few  of  the  stoneworts  (Char- 
aceae)  are  in  form  and  size  comparable  with  the  higher 
plants. 

Many  algae  are  unicellular;  more  are  loose  aggre- 
gates of  cells  functioning  independently ;  a  few  are 
well   integrated   bodies   of  mutually   dependent   cells. 

*Volvox  in  autumn  in  waters  over  submerged  meadows  of  water  weed. 

f  Dinobryon  in  spring  in  shallow  ponds.  . 

XTrichodesmium  erythrceum  gives  to  the  Red  Sea  the  tint  to  which  its 
name  is  due.  The  little  crustacean,  Diaptomus,  often  gives  a  reddish  tint  to 
woodland  pools. 


102 


Aquatic   Organisms 


The  cells  sometimes  form  irregular  masses,  with  more  or 
less  gelatinous  investiture.  Often  they  form  simple 
threads  or  filaments,  or  flat  rafts,  or  hollow  spheres. 
Algal  filaments  are  sometimes  simple,  sometimes 
branched;  sometimes  they  are  cylindric,  sometimes 
tapering;  sometimes  they  are  attached  and  grow  at  the 
free  end  only;  sometimes  they  grow  throughout;  some- 
times they  "are  free,  sometimes  wholly  enveloped  in 
t  ransparent  gelatinous  envelopes.  And  the  form  of  the 
ends,  the  sculpturing  and  ornamentation  of  the  walls  and 
the  distribution  of  chlorophyll  and  other  pigments  are 
various  beyond  all  enumerating,  and  often  beautiful 
beyond  description.  We  shall  attempt  no  more,  there- 
fore, in  these  pages  than  a  very  brief  account  of  a  few 
of  the  commoner  forms,  such  as  the  general  student  of 
fresh  water  life  is  sure  to  encounter;  these  we  will 
call  by  their  common  names,  in  so  far  as  such  names 
are  available. 

The  flagellates — We  will  begin  with  this  group  of 
synthetic  forms,  most  of  which  are  of  microscopic  size 
and  many  of  which  are  exceedingly  minute.  That 
some  of  them  are  considered  to  be  animals  (Mastigo- 
phora)  need  not  deter  us  from  considering  them  all 
together,  suiting  our  method  to  our  convenience.  The 
group  overspreads  the  undetermined  borderland  be- 
tween plant  and  animal  kingdoms.  Certain  of  its 
members  (Euglena)  appear  at  times  to  live  the  life  of  a 
green  plant,  feeding  on  mineral  solutions  and  getting 
energy  from  the  sunlight;  at  other  times,  to  feed  on 
organic  substances  and  solids  like  animals.  The  more 
common  forms  live  as  do  the  algae.  All  the  members  of 
the  group  are  characterized  by  the  possession  of  one  or 
more  living  protoplasmic  swimming  appendages,  called 
flagella,  whence  the  group  name.  Each  flagellum  is 
long,   slender  and  transparent,   and  often  difficult  of 


Flagellates 


103 


observation,  even  when  the  jerky  movements  of  the 
attached  cell  give  evidence  of  its  presence  and  its 
activity.  It  swings  in  front  of  the  cell  in  long  serpen- 
tine curves,  and  draws  the  cell  after  it  as  a  boy's  arms 
draw  his  body  along  in  swimming. 

Many  flagellates  are  permanently  unicellular;  others 
remain  associated  after  repeated  divisions,  forming 
colonies  of  various  forms,  some  of  which  will  be  shown  in 
accompanying  figures. 

Carteria — This  is  a  very  minute  flagellate  of  spherical 
form  and  bright  green  in  color  (fig.  30a).  It  differs 
from  other  green  flagellates  in  having  four  flagella :  the 
others  have  not  more  than  two.  It  is  widely  distrib- 
uted in  inland  waters,  where  it  usually  becomes  more 
abundant  in  autumn,  and  it  appears  to  prefer  slow 
streams.  Kofoid's  notes  concerning  a  maximum  occur- 
rence in  the  Illinois  River  are  well  worth  quoting : 

"The  remarkable  outbreak  of  Carteria  in  the  autumn 
of  1907  was  associated  with  unusually  low  water,  and 


Fig.  30.     Flagellates. 

a,  Carteria;  b,  Spharella;  c,  Euglena;  d,  Trachelomonas;  e,  Pandorina;  f.  Glenodinium; 
g,  Synura;  h,  and  i,  Dinobryon;  a  colony  as  it  appears  under  low  power  of  the  microscope 
and  a  single  individual  highly  magnified;  /,  Ceratium,  (Reversed  left  for  right  in  copying.) 


104  Aquatic  Organism: 


concentration  of  sewage,  and  decrease  of  current.  The 
water  of  the  stream  was  of  a  livid  greenish  yellow  tinge. 
*  *  *  The  distribution  of  Carteria  in  the  river  was 
remarkable.  It  formed  great  bands  or  streaks  visible 
neat*  the  surface,  or  masses  which  in  form  simulated 
cloud  effects.  The  distribution  was  plainly  uneven, 
giving  a  banded  or  mottled  appearance  to  the  stream. 
The  bands,  10  to  15  meters  in  width,  ran  with  the 
channel  or  current,  and  their  position  and  form  were 
plainly  influenced  by  these  factors.  No  cause  was 
apparent  for  the  mottled  regions.  This  phenomenon 
stands  in  somewhat  sharp  contrast  with  the  usual 
distribution  of  waterbloom  upon  the  river,  which  is 
generally  composed  largely  of  Euglena.  This  presents 
a  much  more  uniform  distribution,  and  unlike  Carteria, 
is  plainly  visible  only  when  it  is  accumulated  as  a  super- 
ficial scum  or  film.  Carteria  was  present  in  such  quan- 
tity that  its  distribution  was  evident  at  lower  levels  so 
far  as  the  turbidity  would  permit  it  to  be  seen.  It 
afforded  a  striking  instance  of  marked  inequalities  in 
distribution." 

Similar  green  flagellates  of  wide  distribution  are 
Chlamydomonas  and  Sphaerella  (fig.  306)  commonly 
found   in  rainwater  pools. 

Certain  aggregates  of  such  cells  into  colonies  are  very 
beautiful  and  interesting.  Small  groups  of  such  green 
cells  are  held  together  in  flat  clusters  in  Gonium  and 
Platydorina,  or  in  a  hollow  sphere,  with  radiating 
flagella  that  beat  harmoniously  to  produce  a  regular 
rolling  locomotion  in  Pandorina  (fig.  30  e),  Eudorina 
and  Vol  vox. 

Volvox — The  largest  and  best  integrated  of  these 
spherical  colonies  is  Volvox  (fig.  31).  Each  colony  may 
consist  of  many  thousands  of  cells,  forming  a  sphere 
that  is  readily  visible  to  the  unaided  eye.     It  rotates 


Volvox 


IO: 


constantly  about  one  axis,  and  moves  forward  therefore 
through  the  water  in  a  perfectly  definite  manner. 
Moreover,  the  "eye  spots"  or  pigment  flecks  of  the 
individual  cells  are  larger  on  the  surface  that  goes  fore- 


Fig.  31.     Volvox,  showing  young  colonies  in  all  stages  of  development. 

most.  Sex  cells  are  fully  differentiated  from  the 
ordinary  body  cells.  Nevertheless,  new  colonies  are 
ordinarily  reproduced  asexual ly.  They  develop  from 
single  cells  of  the  old  colony  which  slip  inward  some- 
what below  the  general  level  of  the  body  cells,  repeat- 
edly divide,  (the  mass  assuming  spherical  form), 
differentiate  a  full  complement  of  flagella,  a  pair  to  each 
cell,  and  then  escape  to  the  outer  world  by  rupturing 
the  gelatinous  walls  of  the  old  colony.     Many  develop- 


io6 


Aquatic  Organisms 


ing  colonics  are  shown  within  the  walls  of  the  old  ones 
in  the  figure. 

(  >fu  n,  when  a  weed-carpeted  pond  shows  a  tint  of 
1  night  transparent  green  in  autumn,  a  glass  of  the  water, 
clipped  and  held  to  the  light,  will  be  seen  to  be  filled 
with  these  rolling  emerald  spheres. 

Euglena  Several  species  of  this  genus  (fig.  30c)  are 
common  inhabitants  of  slow  streams  and  pools.  They 
are  all  most  abundant  in  mid-summer,  being  apparently- 
attuned  to  high  tempera- 
tures. They  are  common 
constituents  of  the  water- 
bloom  that  forms  on  the 
surface  of  slow  streams. 
Figure  1  (p.  15)  shows  such 
a  situation,  where  they  re- 
cur every  year  in  June.  Cer- 
tain of  them  are  common  in 
pools  at  sewer  outlets, 
where  bloodworms  dwell  in 
the  bottom  mud.  When 
abundant  in  such  places 
they  give  to  the  water  a 
livid  green  color.  Their 
great  abundance  makes  them  important  agents  in 
converting  the  soluble  stuffs  of  the  water  into  food 
for  rotifers  and  other  microscopic  animals. 

Dinobryon — This  minute,  amber-tinted  flagellate 
forms  colonies  on  so  unique  a  plan  (fig.  30/z)  they  are 
not  readily  mistaken  for  anything  else  under  the  sun. 
Each  individual  is  enclosed  in  an  ovoid  conic  case  or 
lorica,  open  at  the  front  where  two  flagella  protrude 
(fig.  307)  and  many  of  them  are  united  together  in  branch- 
ing,   a  more   or  less  tree-like   colony.     Since  flagella 


Fig.  32.     A  Dinobryon  colony. 


The  Flagellates  107 


always  draw  the  body  after  them,  these  colonies  swim 
along  with  open  ends  forward,  apparently  in  defiance 
of  all  the  laws  of  hydromechanics,  rotating  slowly  on 
the  longitudinal  axis  of  the  colony  as  they  go.  Dino- 
bryon  is  of  an  amber  yellow  tint,  and  often  occurs  in 
such  numbers  as  to  lend  the  same  tint  to  the  water  it 
inhabits.  It  attains  its  maximum  development  at 
low  temperatures.  In  the  cooler  waters  of  our  larger 
lakes  it  is  present  in  some  numbers  throughout  the  year, 
though  more  abundant  in  winter.  Kofoid  reports  it  as 
being  "sharply  limited  to  the  period  from  November  to 
June"  in  Illinois  River  waters.  Its  sudden  increase 
there  at  times  in  the  winter  is  well  illustrated  by  the 
pulse  of  1899,  when  the  numbers  of  individuals  per 
cubic  meter  of  water  in  the  Illinois  River  were  on  suc- 
cessive dates  as  follows: 

Jan.  10th,  1,500 

Feb.     7th,        6,458,000 

11     14th,      22,641,440 

followed  by  a  decline,  with  rising  of  the  river. 

Dinobryon  often  develops  abundantly  under  the  ice. 
Its  optimum  temperature  appears  to  be  near  o°  C.  It 
thus  takes  the  place  in  the  economy  of  the  waters  that 
is  filled  during  the  summer  by  the  smaller  green 
flagellates. 

Synura  (fig.  30^)  is  another  winter  flagellate,  similar 
in  color  and  associated  with  Dinobryon,  much  larger 
in  size.  Its  cells  are  grouped  in  spherical  colonies 
united  at  the  center  of  the  sphere,  and  equipped  on  the 
outer  ends  of  each  with  a  pair  of  flagella,  which  keep  the 
sphere  in  rolling  locomotion.  The  colonies  appear  at 
times  of  maximum  development  to  be  easily  disrupted, 
and  single  cells  and  small  clusters  of  cells  are  often  found 
along  with  well  formed  colonies.  Synura  when  abund- 
ant often  gives  to  reservoir  waters  an  odor  of  cucumbers, 


ioS 


A q ua tic   Organisms 


and  a  singularly  persistent  bad  flavor,  and  under  such 
circumstances  it  becomes     a  pest  in  water  supplies. 

Glenodinium  (fig.  30/),  Peridinium,  and  Ceratium 
(fig.  30/)  are  three  brownish  shell-bearing  flagellates  of 
wide  distribution  often  locally  abundant,  especially  in 
spring  and  summer.  These  all  have  one  of  the  two  long 
flagella  laid  in  a  transverse  groove  encircling  the  body, 

the  other  flagellum  free  (fig.  33). 
Glenodinium  is  the  smallest, 
Ceratium,  much  the  largest. 
Glenodinium  has  a  smooth 
shell,  save  for  the  grooves  where 
the  flagella  arise.  Peridinium 
has  a  brownish  chitinous  shell, 
divided  into  finely  reticulate 
plates.  Ceratium  has  a  heavy 
grayish  shell  prolonged  into 
several  horns. 

On  several  occasions  in  spring 
we  have  seen  the  waters  of  the 
Gym  Pond  on  the  Campus  at 
Lake  Forest  College  as  brown 
as  strong  tea  with  a  nearly  pure 
culture  of  Peridinium  and  con- 
currently therewith  we  have 
seen  the  transparent  phantom-larvae  of  the  midge 
Co  ret  lira  in  the  same  pond  all  showing  a  conspicuous 
brown  line  where  the  alimentary  canal  runs  through 
the  body,  this  being  packed  full  of  Peridinia. 

Trachelomonas  (fig.  30  d)  is  a  spherical  flagellate  hav- 
ing a  brownish  shell  with  a  short  flask-like  neck  at  one 
side  whence  issues  a  single  flagellum.  This  we  have 
found  abundantly  in  pools  that  were  rich  in  oak  leaf 

infusions. 


Fig.  33.  Ceratium  (The  trans- 
verse groove  shows  plainly, 
but  neither  flagellum  shows 
in  the  photograph.) 


Diatoms 


109 


Diatoms — Diatoms  are  among  the  most  abundant  of 
living  things  in  all  the  waters  of  the  earth.  They  occur 
singly  and  free,  or  attached  by  gelatinous  stalks,  or 


Fig.  34.     Miscellaneous  diatoms,  mostly  species  of  Navicula;  the  filaments 
are  blue-green  algae,  mostly  Oscillator hi. 

aggregated  together  in  gelatinous  tubes,  or  compactly 
grouped  in  more  or  less  coherent  filaments.  All  are 
of  microscopic  size.  They  are  most  easily  recognized  by 
their  possession  of  a  box-like  shell,  composed  of  two 
valves,  with  overlapping  edges.  These  valves  are 
stiffened  by  silica  which  is  deposited  in  their  outer  walls, 
often  in  beautiful  patterns.    The  opposed  edges  of  the 


no  Aquatic  Organisms 


valves  are  connected  by  a  membraneous  portion  of  the 
cell  wall  known  as  the  girdle.  A  diatom  may  appear 
very  different  viewed  from  the  face  of  the  valve,  or  from 
the  girdle  (see  fig.  35a  and  b,  or  j  and  k).  They  are 
circular-like  pill-boxes  in  one  great  group,  and  more  or 
less  elongate  and  bilateral  in  the  others. 

Diatoms  are  rarely  green  in  color.  The  chlorophyll 
in  them  is  suffused  by  a  peculiar  yellowish  pigment 
known  as  diatomin,  and  their  masses  present  tints  of 
ami  >er,  of  ochre,  or  of  brown ;  sometimes  in  masses  they 
appear  almost  black.  The  shells  are  colorless;  and, 
bring  composed  of  nearly  pure  silica,  they  are  well 
nigh  indestructible.  They  are  found  abundantly  in 
guano,  having  passed  successively  through  the  stomachs 
of  marine  invertebrates  that  have  been  eaten  by  fishes, 
that  have  been  eaten  by  the  birds  responsible  for  the 
guano  deposits,  and  having  repeatedly  resisted  diges- 
tion and  all  the  weathering  and  other  corroding  effects 
of  time.  They  abound  as  fossils.  Vast  deposits  of 
^  them  compose  the  diatomaceous  earths.  A  well-known 
bed  at  Richmond,  Va.,  is  thirty  feet  in  thickness  and  of 
vast  extent.  Certain  more  recently  discovered  beds 
in  the  Rocky  Mountains  attain  a  depth  of  300  feet. 
Ehrenberg  estimated  that  such  a  deposit  at  Biln  in 
Bohemia  contained  40,000,000  diatom  shells  per  cubic 
inch. 

Singly  they  are  insignificant,  but  collectively  they  are 
very  important,  by  reason  of  their  rapid  rate  of  increase, 
and  their  ability  to  grow  in  all  waters  and  at  all  ordinary 
temperatures.  Among  the  primary  food  gatherers 
of  the  water  world  there  is  no  group  of  greater  import- 
ance. 

In  figure  35  we  present  more  or  less  diagrammatically 
a  few  of  the  commoner  forms.  The  boat -shaped,  freely 
moving  cells  of  Navicula  (a,  b,  c)  are  found  in  every 
pool.     One  can  scarcely  mount  a  tuft  of  algae,  a  leaf 


Diatoms 


i  ii 


of  water  moss  or  a  drop  of  sediment  from  the  bottom 
without  finding  Naviculas  in  the  mount.  They  are 
more  abundant  shoreward  than  in  the  open  waters  of 
the  lake.  The  ''white-cross  diatom"  Stauroneis  (d),  is  a 
kindred  form,  easily  recognizable  by  the  smooth  cross- 
band  which  replaces  the  middle  nodule  of  Navicula. 


£ 


Fig.   35.     Diatoms. 

a,  valve  view  showing  middle  and  end  nodules,  and  b,  girdle  view  of  Navicula.  c,  another 
species  of  Navicula;  d,  Stauroneis;  e,  valve  view  and  f,  girdle  view  of  Tabellaria;  g, 
Synedra;  h,  Gyrosigma;  i,  a  gelatinous  cord-like  cluster  of  Encyonema  showing  girdle 
view  of  nine  individuals  and  valve  view  of  three.  3,  valve  view  and  k,  girdle  view  of 
Melosira;  I,  Stephanodiscus;  m,  Meridion  colony,  with  a  single  detached  individual  shown 
in  valve  view  below;  n,  a  small  colony  of  Asterionella;  o,  valve  view,  and  p,  girdle  view 
of  Camplylodiscus;    q,  cluster  of  Cocconema.     (Figures  mostly  after  Wolle). 

Tabellaria  (e  and  /)  is  a  thin  flat-celled  diatom  that 
forms  ribbon-like  bands,  the  cells  being  apposed,  valve 
to  valve.  Often  the  ribbons  are  broken  into  rectangu- 
lar blocks  of  cells  which  hang  together  in  zig-zag  lines 
by  the  corners  of  the  rectangles.  The  single  cell  is  long- 
rectangular  in  girdle  view  (slightly  swollen  in  the  middle 
and  at  each  end,  as  shown  at  e,  in  valve  view),  and  is 
traversed  by  two  or  more  intermediate  septa.  Tabel- 
laria abounds  in  the  cool  waters  of  our  deeper  northern 
lakes,  at  all  seasons  of  the  year.  It  is  much  less  common 
in  streams. 


H2  A  qua  tic  Organ  isms 


The  slender  cells  of  the"  needle  diatoms,"  Synedra  (g), 
are  common  in  nearly  all  waters  and  at  all  seasons. 
They  are  perhaps  most  conspicuously  abundant  when 
found,  as  often  happens,  covering  the  branches  of  some 
tufted  algae,  such  as  Cladophora,  in  loose  tufts  and 
fascicles,  all  attached  by  one  end. 

Gyrosigma  (//■)  is  nearly  allied  to  Navicula  but  is 
easily  recognized  by  the  gracefully  curved  outlines  of  its 
more  or  less  S-shaped  shell.  The  sculpturing  of  this 
shell  (not  shown  in  the  figure)  is  so  fine  it  has  long  been  a 
classic  test-object  for  the  resolving  power  of  microscopic 
lenses.  Gyrosigma  is  a  littoral  associate  of  Navicula, 
but  of  much  less  frequent  occurrence. 

Ericyoriema  (i)  is  noteworthy  for  its  habit  of  develop- 
ing in  long  unbranched  gelatinous  tubes.  Sometimes 
these  tubes  trail  from  stones  on  the  bottom  in  swift 
streams.  Sometimes  they  radiate  like  delicate  filmy 
hairs  from  the  surfaces  of  submerged  twigs  in  still 
water.  The  tubes  of  midge  larvae  shown  in  figure  1 34 
were  encircled  by  long  hyaline  fringes  of  Encyonema 
filaments,  which  constituted  the  chief  forage  of  the 
larvae  in  the  tubes  and  which  were  regrown  rapidly 
after  successive  grazings.  When  old,  the  cells  escape 
from  the  gelatine  and  are  found  singly. 

The  group  of  diatoms  having  circular  shells  with 
radially  arranged  sculpturing  upon  the  valves  is  repre- 
sented by  Melosira  (7  and  k)  and  Stephanodiscus  (I)  of 
our  figure.  Melosira  forms  cylindric  filaments,  whose 
constituent  cells  are  more  solidly  coherent  than  in 
other  diatoms.  Transverse  division  of  the  cells  in- 
creases the  length  of  the  filaments,  but  they  break  with 
the  movement  of  the  water  into  short  lengths  of  usually 
about  half  a  dozen  cells.  They  are  eommon  in  the 
open  water  of  lakes  and  streams,  and  are  most  abundant 
at  the  higher  temperatures  of  midsummer.  Cyclotella 
is  a  similar  form  that  does  not,  as  a  rule,  form  filaments. 


Diatoms 


113 


Its  cells  are  very  small,  and  easily  overlooked,  since 
they  largely  escape  the  finest  nets  and  are  only  to  be 


Fig.  36.    A  nearly  pure  culture  of  Meridion,  showing  colonies  of 
various  sizes. 

gathered  from  the  water  by  filtering.  Often,  however, 
their  abundance  compensates  for  their  size.  Kofoid 
found  their  average  number  in  the  waters  of  the  Illinois 


U4  Aquatic  Organisms 

River  to  be  36,558,462  per  cubic  meter  of  water,  and  he 
considered  them  as  one  of  the  principal  sources  of  food 
supply  of  Entomostraca  and  other  microscopic  aquatic 
animals.  Stephanodiscus  (I)  is  distinguished  by  the 
long,  hyaline  filaments  that  radiate  from  the  ends  of  the 
box,  and  that  serve  to  keep  it  in  the  water.  A  species 
of  Stephanodiscus  having  shorter  and  more  numerous 
fi  laments  is  common  in  the  open  waters  of  Cayuga  Lake 
in  spring. 

The  cells  of  Meridiem  are  wedge-shaped,  and  grouped 
together  side  by  side,  they  form  a  flat  spiral  ribbon  of 
very  variable  length,  sometimes  in  one  or  more  com- 
plete turns,  but  oftener  broken  into  small  segments. 
This  form  abounds  in  the  brook  beds  about  Ithaca, 
covering  them  every  winter  with  an  amber -tinted  or 
brownish  ooze,  often  of  considerable  thickness.  It 
appears  to  thrive  best  when  the  temperature  of  the 
water  is  near  o°  C.  Its  richest  growth  is  apparent  after 
the  ice  leaves  the  brooks  in  the  spring.  As  a  source  of 
winter  food  for  the  lesser  brook-dwelling  animals,  it  is 
doubtless  of  great  importance.  A  view  of  a  magni- 
fied bit  of  the  ooze  is  shown  in  figure  36. 

The  colonies  of  Asterionella  (n)  whose  cells,  adhering 
at  a  single  point,  radiate  like  the  spokes  of  a  wheel,  are 
common  in  the  open  waters  of  all  our  lakes  and  large 
streams.  It  is  a  common  associate  of  Cyclotella,  and  of 
Tabellaria  and  other  band-forming  species,  and  is  often 
more  abundant  than  any  of  these.  The  open  waters  of 
Lake  Michigan  and  of  Cayuga  Lake  are  often  yellowish 
tinted  because  of  its  abundance  in  them.  Late  spring 
and  fall  (especially  the  former)  after  the  thermal  over- 
turn and  complete  circulation  of  the  water  are  the 
seasons  of  its  maximum  development.  Asterionella 
abounds  in  water  reservoirs,  where,  at  its  maxima,  it 
sometimes  causes  trouble  by  imparting  to  the  water  an 
aromatic  or  even  a  decidedly  "fishy"  odor  and  an 
unpleasant  taste. 


Diatoms 


ii5 


Campylodiscus  (0  and  p)  is  a  saddle-shaped  diatom  of 
rather  local  distribution.  It  is  found  abundantly  in  the 
ooze  overspreading  the  black  muck  bottom  of  shallow 
streams  at  the  outlet  of  bogs.  In  such  places  in  the 
upper  reaches  of  the  tributaries  of  Fall  Creek  near 
Ithaca  it  is  so  abundant  as  to  constitute  a  large  part  of 
the  food  of  a  number  of  denizens  of  the  bottom  mud — ■ 
notably  of  midge  larvae,  and  of  nymphs  of  the  big 
Mayfly,  Hexagenia. 

These  are  a  few — a  very  few — of  the  more  important 
or  more  easily  recognized  diatoms.  Many  others  will 
be  encountered  anywhere,  the  littoral  forms  especially 
being  legion.  Stalked  forms  like  Cocconema  (fig.  355  and 
fig-  37)  will  be  found  attached  to  every  solid  support. 
And  minute  close-clinging  epiphytic  diatoms,  like 
Cocconeis  and  Epithemia  will  be 
found  thickly  besprinkling  the 
green  branches  of  many  sub- 
merged aquatics.  These  adhere 
closely  by  the  flat  surface  of  one 
valve  to  the  epidermis  of  aquatic 
mosses. 

In  open  lakes,  also,  there  are 
other  forms  of  great  importance, 
such  SLsD-iatoma,  Fragillaria,  etc., 
growing  in  flat  ribbons,  as  does 
Tabellaria.  It  is  much  to  be 
regretted  that  there  are,  as  yet, 
no  readily  available  popular 
guides  to  the  study  of  a  group, 
so  important  and  so  interesting. 

Equipped  with  a  plancton  net  and  a  good  microscope, 
the  student  would  never  lack  for  material  or  for  prob- 
lems of  fascinating  interest. 


Fig.  37.     A  stalked  colony 
Cocconema. 


n6  Aquatic  Organisms 


Desmids — This  is  a  group  of  singularly  beautiful 
unicellular  fresh-water  algae.  Desmids  are,  as  a  rule, 
of  a  refreshing  green  color,  and  their  symmetry  of  form 
and  delicacy  of  sculpturing  are  so  beautiful  that  they 
have   always   been   in   favor  with   microscopists.     So 


Fig.  38.     A  good  slide-mount  from  a  Closterium  culture 
as  it  appears  under  a  pocket  lens.     Two  species. 

numerous  are  they  that  their  treatment  has  of  late  been 
relegated  to  special  works.  Here  we  can  give  only  a 
few  words  concerning  them,  with  illustrations  of  some 
of  the  commoner  forms. 

Desmids  may  be  recognized  by  the  presence  of  a  clear 
band  across  the  middle  of  each  cell,  (often  emphasized 
by  a  corresponding  median  constriction)  dividing  it 
symmetrically  into  two  semicells.  Superficially  they 
appear  bicellular  ("especially  in  such  forms  as  Cylindro- 


Desmids 


i  i 


cystis,  fig.  40  e),  but  there  is  a  single  nucleus,  and  it  lies 
in  the  midst  of  the  transparent  crossband.  The  larger 
ones,  such  as  Closterium  (fig.  38)  may  be  recognized  with 
the  unaided  eye,  and  may  be  seen  clearly  with  a  pocket 
lens.  Because  it  will  grow  per- 
ennially in  a  culture  jar  in  a 
half -lighted  window,  Closterium 
is  a  very  well  known  labora- 
tory type. 

Division  is  transverse  and  sep- 
arates between  the  semicells. 
Its  progress  in  Closterium  is 
shown  in  figure  39,  in  a  series  of 
successive  stages  that  were  photo- 
graphed between  10  p.  m.  and  3 
A.  M.  Division  normally  occurs 
only  at  night. 

In  a  few  genera  {Gonatozygon, 
(fig.  40a)  Desmidium,  etc.)  the 
cells  after  division  remain  at- 
tached, forming  filaments. 

Desmids  are  mainly  free  float- 
ing and  grow  best  in  still  waters. 
They  abound  in  northern  lakes 
and  peat  bogs.  They  prefer  the 
waters  that  run  off  archaean 
rocks  and  few  of  them  flourish 
in  waters  rich  in  lime.  A  few 
occur  on  mosses  in  the  edges  of 
waterfalls,  being  attached  to  the 
mosses  by  a  somewhat  tenacious  gelatinous  invest- 
ment. One  can  usually  obtain  a  fine  variety  of 
desmids  by  squeezing  wisps  of  such  water  plants 
as  Utricularia  and  Sphagnum,  over  the  edge  of  a 
dish,  and  examining  the  run-off.  The  largest  genus  of 
the  group  and  also  one  of  the  most  widespread   is 


Fig.  39.  Photomicrographs 
of  a  Closterium  dividing. 
The  lowermost  figure  is 
one  of  the  newly  formed 
daughter  cells,  not  yet 
fully  shaped. 


nS 


Aquatic  Organisms 


Filamentous  Conjugates 


II<) 


Cosmarium  (fig.  40  s).  The 
most  bizarre  forms  are  found 
in  the  genera  Micrasterias  (figs. 
40  q  and  r)  and  Staurastrum. 
These  connect  in  form 
through  Euastrum  (fig.  40  0) 
Tetmemorus  (fig.  40  n)  Netrium 
(fig.  40  d),  etc.,  with  the  sim- 
pler forms  which  have  little 
differentiation  of  the  poles  of 
the  cell;  and  these,  especially 
Spirotaenia  (fig.  40  b)  and  Gon- 
atozygon  (fig.  40  a)  connect 
with  the  filamentous  forms 
next  to  be  discussed. 

The  Filamentous  Conjugates 
— This  is  the  group  of  fila- 
mentous algae  most  closely 
allied  with  the  desmids.  It 
includes  three  common  genera 
(fig.  41) — Spirogyra,  Zygnema, 
and  Mougeotia.  The  first  of  these  being  one  of 
the  most  widely  used  of  biological  "types"  is  known 
to  almost  every  laboratory  student.  Its  long,  green, 
unbranched,  slippery  filaments  are  easily  recognized 
among  all  the  other  greenery  of  the  water  by  their 
beautiful  spirally-wound  bands  of  chlorophyl.  The 
other  common  genera  have  also  distinctive  chlorophyl 
arrangement.  Zygnema  has  a  pair  of  more  or  less 
star-shaped  green  masses  in  each  cell,  one  on  either  side 
of  the  central  nucleus.      In  Mougeotia  the  chlorophyl 


Fig.  41.     Filamentous  con- 
jugates. 

a.  Spirogyra;  b,  flat  view,  anil  c, 
edgewise  view  of  the  chlorophyl 
plate  in  cells  of  Mougeotia,  d, 
Zygnema. 


a,  a  little  more  than  two  cells  g  Docidium  baculum 

from  a  filament  of  Gonatozygon  h  Docidium  undulatum 

b  Spirotania  i  Closterium  pronum 

c  Mesotanium  j  Closterium  rostratum 

d  Netrium  k  Closterium  moniliferum 

e  Cylindrocystis  I  Closterium  ehrenbergi 

f  Penium  m  Pleurotanium 


n  Tetmemorus 

o  Euastrum  didelta 

p  Euastrum  verrucosum 

q  Micrasterias  oscitans 

r  Micrasterias  americana:  (for 

a  third  species  see  page  53)- 
s  Cosmarium,  face  view,   and 

outline  as  seen  from  the  side 


120  Aquatic  Organisms 


is  in  a  median  longitudinal  plate,  which  can  rotate  in 
the  cell :  it  turns  its  thin  edge  upward  to  the  sun,  but 
lies  1  (roadside  exposed  to  weak  light.  Spirogyra  is 
the  most  abundant,  especially  in  early  spring  where  it 
is  f<  >undin  the  pools  ere  the  ice  has  gone  out.  All,  being 
unattached  (save  as  they  become  entangled  with  rooted 
aquatics  near  shore),  prefer  quiet  waters.  Immense 
accumulations  of  their  tangled  filaments  often  occur  on 
the  shores  of  shallow  lakes  and  ponds,  and  with  the 
advance  of  spring  and  subsidence  of  the  water  level, 
these  are  left  stranded  upon  the  shores.  They  chiefly 
compose  the  "blanket -moss"  of  the  fishermen.  They 
settle  upon  and  smother  the  shore  vegetation,  and  in 
their  decay  they  sometimes  give  off  bad  odors.  Some- 
times they  are  neaped  in  windrows  on  shelving  beaches, 
and  left  to  decay. 

We  most  commonly  see  them  floating  at  the  surface 
in  clear,  quiet,  spring-fed  waters  in  broad  filmy  masses 
of  yellowish  green  color,  which  in  the  sunlight  fairly 
teem  with  bubbles  of  liberated  oxygen.  These  dense 
masses  of  filaments  furnish  a  home  and  shelter  for  a 
number  of  small  animals,  notably  Haliplid  beetle  larvae 
and  punkie  larvae  among  insects;  and  entanglement 
by  them  is  a  peril  to  the  lives  of  others,  notably  certain 
Mayfly  larvae  {Blasturus).  The  rather  large  filaments 
afford  a  solid  support  for  hosts  of  lesser  sessile  algae; 
and  their  considerable  accumulation  of  organic  contents 
is  preyed  upon  by  many  parasites.  Their  role  is  an 
important  one  in  the  economy  of  shoal  waters,  and  its 
importance  is  due  not  alone  to  their  power  of  rapid 
gr<  >wth,  but  also  to  their  staying  qualities.  They  hold 
their  own  in  all  sorts  of  temporary  waters  by  develop- 
ing protected  reproductive  cells  known  as  zygospores, 
which  are  able  to  endure  temporary  drouth,  or  other 
untoward  conditions.  Zygospores  are  formed  by  the 
fusion  of  the  contents  of  two  similar  cells  (the  process 


Siphon  Algae 


121 


is  known  as  conjugation,  whence  the  group  name)  and 
the  development  of  a  protective  wall  about  the  result- 
ing reproductive  body.  This  rests  for  a  time  like  a  seed, 
and  on  germinating,  produces  a  new  filament  by  the 
ordinary  process  of  cell  division.  These  filamentous 
forms  share  this  reproductive  process  with  the  desmids, 
and  despite  the  differences  in  external  aspect  it  is  a 
strong  bond  of  affinity  between  the  two  groups. 

The  siphon  algce — This 
peculiar  group  of  green 
algae  contains  a  few  forms 
of  little  economic  con- 
sequence but  of  great 
botanical  interest.  The 
plant  body  grows  out  in 
long  irregularly  branch- 
ing filaments  which, 
though  containing  many 
nuclei,  lack  cross  par- 
titions. The  filaments 
thus  resemble  long  open 
tubes,  whence  the  name 
siphon  algae.  There  are  two  common  genera  Vau- 
cheria and  Botrydium  (fig.  42).  Both  are  mud-lov- 
ing, and  are  found  partly  out  of  the  water  about  as 
often  as  wholly  immersed.  Vaucheria  develops  long, 
crooked,  extensively  interlaced  filaments  which  occur  in 
dense  mats  that  have  suggested  the  name  ' 'green  felt." 
These  felted  masses  are  found  floating  in  ponds,  or 
dying  on  wet  soil  wherever  there  is  light  and  a  con- 
stantly moist  atmosphere  (as,  for  example,  in  green- 
houses, where  commonly  found  on  the  soil  in  pots). 
Botrydium  is  very  different  and  much  smaller.  It  has 
an  oval  body  with  root-like  branches  growing  out  from 
the  lower  end  to  penetrate  the  mud.  It  grows  on  the 
bottom  in  shoal  waters,  and  remains  exposed  on  the 


Fig.  42.     Two  siphon  algae. 

A ,  Botrydium;    B,  a  small  fruiting  portion  of  a 
filament  of  Vaucheria.;  ov,  ovary;  sp,  spermary. 


122 


Aquatic  Organisms 


mud  after  the  water  has  receded,  dotting  the  surface 
thickly,  as  with  greenish  beads  of  dew. 

The  water  net  and  its  allies — The  water  net  (Hydro- 
diet  yon)  wherever  found,  is  sure  to  attract  attention  by 
its  curious  form.  It  Is  a  cylindric  sheet  of  lace-like 
tissue,  composed  of  slender  green  cells  that  meet  at 


A 

k^^mI 

^QhI 

fVlPk 

^     h\W 

wU. 

jBi? 

QiJ 

W^J 

m 

1 

Fig.  43.     A  rather  irregular  portion  of  a  sheet  of  water  net 
(Hydrodictyon) 

their  ends,  usually  by  threes,  forming  hexagonal  meshes 
like  bobbinet  (fig.  43).  Such  colonies  may  be  as  broad 
as  one's  hand,  or  microscopic,  or  of  any  intermediate 
size;  for  curiously  enough,  cell  division  and  cell 
growth  are  segregated  in  time.  New  colonies  are 
formed  by  repeated  division  of  the  contents  of  single 


The  Water  Xcts 


123 


cells  of  the  old  colonies.  A  new  complete  miniature 
net  is  formed  within  a  single  cell;  and  after  its  escape 
from  the  old  cell  wall,  it  grows,  not  by  further  division, 
but  by  increase  in  size  of  its  constituent  cells. 

Water  net  is  rather  local  and  sporadic  in  occurrence, 
but  it  sometimes  develops  in  quantities  sufficient  to  fill 
the  waters  of  pools  and  small  ponds. 


Fig.  44.     Pediastrum:     Several  species  from  the 
Cayuga  Lake. 


plancton  of 


Pediastrum  is  a  closely  related  genus  containing  a 
number  of  beautiful  species,  some  of  which  are  common 
and  widespread.  The  cells  of  a  Pediastrum  colony  are 
arranged  in  a  roundish  flat  disc,  and  those  of  the  outer- 
most row  are  usually  prolonged  into  radiating  points. 
Several  species  are  shown  in  figure  44.     In  the  open- 


124 


Aquatic  Organisms 


meshed  species  the  inner  cells  can  be  seen  to  meet  by 
threes  about  the  openings,  quite  as  in  the  water  net; 
1  >ut  the  cells  are  less  elongate  and  the  openings  smaller. 
Five  of  the  seven  specimens  shown  in  the  figure  lack 
these  openings  altogether. 

New  colonics  are  formed  within  single  cells,  as  in 
Hvdrodictyon.  In  our  figure  certain  specimens  show 
marginal  cells  containing  developing  colonies.  One 
shows  an  empty  cell  wall  from  whence  a  new  colony  has 
escaped. 

Other  green  alga? — 
We  have  now  men- 
tioned a  few  of  the 
more  strongly 
marked  groups  of  the 
green  algae.  There 
are  other  forms,  so 
numerous  we  may 
not  even  name  them 
here,  many  of  which 
are  common  and 
widely  dispersed. 
We  shall  have  space 
to  mention  only  a 
few  of  the  more  im- 
portant among  them, 
and    we    trust    that 

the  accompanying  figures  will  aid  in  their  recognition. 
Numerous  and  varied  as  they  are,  we  will  dismiss  them 
from  further  consideration  under  a  few  arbitrary  form 
types. 

i.  Simple  filamentous  forms.  Of  such  sort  are 
llothrix,  CEdogonium,  Conferva,  etc.,  (fig.  45).  Ulo- 
thrix  is  common  in  sunny  rivulets  and  pools,  especially 
in  early  spring,  where  its  slender  filaments  form  masses 


Fig.  45.    Filamentous  Green  AlgEe. 

L'lothrix;  b,  CEdogonium,  showing  characteristic 
annulate  appearance  at  upper  end  of  cell;  c. 
Conferva  (Tribonema);  d,  Draparnaldia.  (After 
West). 


Other  Green  Algae  12, 


half  floating  in  the  water.     The  cells  are  short,  often  no 
longer  than  wide,  and  each  contains  a  single  sheet  of 


Fig.  46.     A  spray  of  Cladophora,  as  it  appears  when 
outspread  in  the  water,  slightly  magnified. 

chlorophyl,  lining  nearly  all  of  its  lateral  wall.  CEdogo- 
muni  is  a  form  with  stouter  filaments  composed  c>f 
much  longer  cells,  within  which  the  chlorophyl  is  dis- 


126 


Aquatic  Organisms 


posed  in  anastomosing  bands.  The  thick  cell  walls, 
some  of  which  show  a  peculiar  cross  striation  near  one 
end  of  the  cell,  are  ready  means  of  recognition  of  the 
members  of  this  great  genus.  The  filaments  are 
attached  when  young,  but  break  away  and  float  freely 
in  masses  in  quiet  waters  when  older;  it  is  thus  they 
are  usually  seen.  Conferva  (Tribonema)  abounds  in 
shallow  pools,  especially  in  spring  time.  Its  filaments 
are  composed  of  elongate  cells  containing  a  number  of 

separate  disc-like  chlor- 
ophyl  bodies.  The  cell 
wall  is  thicker  toward 
the  ends  of  the  cell,  and 
the  filaments  tend  to 
break  across  the  middle, 
forming  pieces  (halves  of 
two  adjacent  cells)  which 
appear  distinctly  H- 
shaped  in  optic  section. 
This  is  a  useful  mark 
for  their  recognition.  It 
will  be  observed  that 
these  then  are  similar 
in  form  and  habits  to 
the  filamentous  conju- 
gates discussed  above, 
but  they  have  not  the 
peculiar  form  of  chlor- 
ophyl  bodies  characteristic  of  that  group.  (Eodgonium 
is  remarkable  for  its  mode  of  reproduction. 

2.  Branching  filamentous  forms — Of  such  sort  are  a 
number  of  tufted  sessile  algae  of  great  importance: 
Cladophora,  which  luxuriates  in  the  dashing  waterfall, 
which  clothes  every  wave-swept  boulder  and  pier  with 
delicate  fringes  of  green,  which  lays  prostrate  its  pliant 
sprays  (fig.  46)  before  each  on-rushing  wave,  and  lifts 


Fig.  47.  Two  species  of  Chactophora, 
represented  by  several  small  hemi- 
spherical colonies  of  C.  pisiformis  and 
one  large  branching  colony  of 
C.    incrassata. 


Other  Green  Ahae 


I27 


them  again  uninjured,  after  the  force  of  the  flood  is 
spent.  And  Chcetophora  (fig.  47;  also  fig.  89  on  p.  182) ; 
which  is  always  deeply  buried  under  a  transparent  mass 


Fig.  48.  Chsetophora  (either  species)  crushed  and  outspread 
in  its  own  gelatinous  covering  and  magnified  to  show  the 
form  of  the  filaments. 


of  gelatin;  which  forms  little  hemispherical  hillocks  of 
filaments  in  some  species,  and  in  one,  extends  outward 
in  long  picturesque  sprays,  but  which  has  in  all  much 
the  same  form  of  plant  body  (fig.  48) — a  close-set  branch- 
ing filament,  with  the  tips  of  some  of  the  branches  ending 
in  a  long  hyaline  bristle-like  point.  Chaetophora  grows 
very  abundantly  in  stagnant  pools  and  ponds  in  mid- 


128 


Aquatic  Organisms 


summer,  adhering  to  every  solid  support  that  offers, 
and  it  is  an  important  part  of  the  summer  food  of  many 
of  the  lesser  herbivores  in  sueh  waters. 

Then  we  must  not  omit  to  mention  two  that,  if  less 
important,  are  certainly  no  less  interesting:  Drapar- 
naldia  (fig.  45^)  which  lets  its  exceedingly  delicate  sprays 
trail  like  tresses  among  the  submerged  stones  in  spring- 


Fig.  49.     Coleochccte  scutata.     "Green  doily." 

fed  rivulets;  and  Colcochcete  (fig.  49),  which  spreads  its 
flattened  branches  out  in  one  plane,  joined  by  their 
edges,  forming  a  disc,  that  is  oftenest  found  attached  to 
the  vertical  stem  of  some  reed  or  bulrush. 

Miscellaneous  lesser  green  algce — Among  other  green 
algae,  which  are  very  numerous,  we  have  space  here  for 
a  mere  mention  of  a  few  of  the  forms  most  likely  to  be 
met  with,  especially  by  one  using  a  plancton  net  in  open 
waters.     These  will  also  illustrate  something  of  the 


Lesser  Green  Algae 


129 


remarkable  diversity  of  form  and  of  cell  grouping  among 
the  lesser  green  algae. 

Botryococcus  grows  in  free  floating  single  or  compound 
clusters  of  little  globose  green  cells,  held  together  in  a 
scanty  gelatinous  investment.  The  clusters  are  suffi- 
ciently grape-like  to  have  suggested  the  scientific  name. 
They  contain,  when  grown,  usually  16  or  32  cells  each. 
They  are  found  in  the  open  waters  of  bog  pools,  lakes, 


Fig.  50.     Miscellaneous  green  algas  (mostly  after  West). 

a,  Botryococcus;  b,  Ccelastrum;  c,  Dictosphczrium;  d,  Kirchnerella; 
e,  Selenastrum;  f,  Ankistrodestnus  falcatus;  g,  Ophiocytium;  k, 
Tetraspora;  i,  Crucigenia;  j,  Scenedesmus;,  k,  Rhicteriella;  I, 
Ankistrodestnus  setigerus;    m,  Oocystis. 

and  streams,  during  the  warmer  part  of  the  season, 
being  most  abundant  during  the  hot  days  of  August. 
When  over-abundant  the  cells  sometimes  become  filled 
with  a  brick-red  oil.  They  occur  sparingly  in  water- 
bloom. 

Dictyosphcerum  likewise  grows  in  more  or  less  spheri- 
cal colonies  of  globose  cells.  The  cells  are  connected 
together  by  dichotomously  branching  threads  and  all 
are  enveloped  in  a  thin  spherical  mass  of  mucus.  The 
colonies  are  free  floating  and  are  taken  in  the  plancton  of 
ponds  and  lakes  and  often  occur  in  the  water-bloom. 


[(/Katie  Organisms 


Ccdastrum  is  another  midsummer  plancton  alga  that 
forms  spherical  colonies  of  from  8  to  32  cells ;  it  has  much 
firmer  and  thicker  cell  walls,  and  the  cells  are  often 
angulate  or  polyhedral.  New  colonies  are  formed  within 
the  walls  of  each  of  the  cells  of  the  parent  colony,  and 
when  well  grown  these  escape  by  rupture  or  dissolution 
of  the  old  cell  wall.  Our  figure  shows  merely  the  out- 
line of  the  cell  walls  of  a  16-celled  colony,  in  a  species 
having  angulate  cells,  between  which  are  open  inter- 
spaces. Kofoid  found  Ccelastrum  occurring  in  a  maxi- 
mum of  10,800,000  per  cubic  meter  of  water  in  the 
Illinois  River  in  August. 

Crucigenia  is  an  allied  form  having  ovoid  or  globose 
cells  arranged  in  a  flat  plate  held  together  by  a  thin 
mucilaginous  envelope.  The  cells  are  grouped  in  fours, 
but  8,  16,  32,  64  or  even  more  may,  when  undisturbed, 
remain  together  in  a  single  flat  colony.  During  the 
warmer  part  of  the  season,  they  are  common  constit- 
uents of  the  fresh-water  plancton,  the  maximum  heat 
of  midsummer  apparently  being  most  favorable  to  their 
development. 

Scenedesmus  is  a  very  hardy,  minute,  green  alga  of 
wide  distribution.  There  is  hardly  any  alga  that 
appears  more  commonly  in  jars  of  water  left  standing 
about  the  laboratory.  When  the  sides  of  the  jar  begin 
to  show  a  film  of  light  yellowish -green,  Scenedesmus 
may  be  looked  for.  The  cells  are  more  or  less  spindle- 
shaped,  sharply  pointed,  or  even  bristle-tipped  at  the 
ends.  They  are  arranged  side  by  side  in  loose  flat  rafts 
of  2,  4  or  8  (oftenest,  when  not  broken  asunder,  of  4) 
cells.  They  are  common  in  plancton  generally,  espec- 
ially in  the  plancton  of  stagnant  water  and  in  that  of 
polluted  streams,  and  although  present  at  all  seasons, 
thev  are  far  more  abundant  in  mid  and  late  summer. 


Lesser  Green  Algae  131 

Kirchnerella  is  a  loose  aggregate  of  a  few  blunt  - 
pointed  U-shaped  cells,  enveloped  in  a  thick  spherical 
mass  of  jelly.  It  is  met  with  commonly  in  the  plancton 
of  larger  lakes.  Selenastrum  grows  in  nearly  naked 
clusters  of  more  crescentic,  more  pointed  cells  which  are 
found  amid  shore  vegetation.  Ankistrodesmus  is  a 
related,  more  slender,  less  crescentic  form  of  more 
extensive  littoral  distribution.  The  slenderest  forms  of 
this  genus  are  free  floating,  and  some  of  them  like  A . 
setigera  (fig.  50  /)  are  met  with  only  in  the  plancton. 

Richteriella  is  another  plancton  alga  found  in  free 
floating  masses  of  a  few  loosely  aggregated  cells.  The 
cells  are  globose  and  each  bears  a  few  long  bristles  upon 
its  outer  face.  Kofoid  found  Richteriella  attaining  a 
maximum  of  36,000,000  per  cubic  meter  of  water  in 
September,  while  disappearing  entirely  at  temperatures 
below  6o°  F. 

Oocystis  grows  amid  shore  vegetation,  or  the  lighter 
species,  in  plancton  in  open  water.  The  ellipsoid  cells 
exist  singly,  or  a  few  are  loosely  associated  together  in  a 
clump  of  mucus.  The  cells  possess  a  firm  smooth  wall 
which  commonly  shows  a  nodular  thickening  at  each 
pole. 

Ophiocytium  is  a  curious  form  with  spirally  coiled 
multinucleate  cells.  The  bluntly  rounded  ends  of  the 
cells  are  sometimes  spine-tipped.  These  cells  some- 
times float  free,  sometimes  are  attached  singly,  some- 
times in  colonies.  Kofoid  found  them  of  variable 
occurrence  in  the  Illinois  River,  where  the  maximum 
number  noted  was  57,000,000  per  cubic  meter  occur- 
ring in  September.  The  optimum  temperature,  as 
attested  by  the  numbers  developing,  appeared  to  be 
about  6o°  F. 

Tetraspora — We  will  conclude  this  list  of  miscellanies 
with  citing  one  that  grows  in  thick  convoluted  strings 


132 


Aquatic  Organisms 


and  loose  ropy  masses  of  gelatin  of  considerable  size. 
These  masses  are  often  large  enough  to  be  recognized 
with  the  unaided  eye  as  they  lie  outspread  or  hang  d<  >wn 
upon  trash  on  the  shores  of  shoal  and  stagnant  waters. 
Within  the  gelatin  are  minute  spherical  bright  green 
cells,  scattered  or  arranged  in  groups  of  fours. 

Blue-Green  Alg je  (Cyanophycece  or  Myxophycea) . 

The  "blue-greens"  are  mainly  freshwater  algae,  of  simple 
forms.  The  cells  exist  singly,  or  embedded  together  in 
loose  gelatinous  envelope  or  adhere  in  flat  rafts  or  in 
filaments.  Their  chlorophyl  is  rather  uniformly  dis- 
tributed over  the  outer  part  of  the  cell  (quite  lacking  the 
restriction  to  specialized  chloroplasts  seen  in  the  true 
green-algae)  and  its  color  is  much  modified  by  the 
presence  of  pigment  (phycocyanin) ,  which  gives  to  the 
cell  usually  a  pronounced  bluish-green,  sometimes,  a 
reddish  color. 

Blue-green  algae  exist  wherever  there  is  even  a  little 
transient  moisture — on  tree  trunks,  on  the  soil,  in 
lichens,  etc. ;  and  in  all  fresh  water  they  play  an  impor- 
tant role,  for  they  are  fitted  to  all  sorts  of  aquatic 
situations,  and  they  are  possessed  of  enormous  reproduc- 
tive capacity.  Among  the  most  abundant  plants  in  the 
water  world  are  the  Anabcenas  (fig.  179),  and  other  blue- 
greens  that  multiply  and  fill  the  waters  of  our  lakes  in 
midsummer,  and  break  in  " water-bloom"  covering  the 
entire  surface  and  drifting  with  high  winds  in  windrows 
on  shore.  Such  forms  by  their  decay  often  give  to  the 
water  of  reservoirs  disagreeable  odors  and  bad  flavors, 
and  so  they  are  counted  noxious  to  water  supplies. 

There  are  many  common  blue-greens,  and  here  we 
have  space  to  mention  but  a  few  of  the  more  common 
forms.  Two  of  the  loosely  colonial  forms  composed  of 
spherical  cells  held  together  in  masses  of  mucus  are 
Ccelosphcerhim  and  Microcystis.     Both  these  are  often 


Blue-green  A I  gee 


1 33 


associated  with  Anabaena  in  the  water-bloom.  Ccelos- 
phaerium  is  a  spherical  hollow  colony  of  microscopic  size. 
It  is  a  loose  association  of  cells,  any  of  which  on  separa- 
tion is  capable  of  dividing  and  producing  a  new  colony. 
Microcystis  (fig.  51-4)  is  a  mass  of  smaller  cells,  a  very 
loose  colony  that  is  at  first  more  or  less  spherical  but 
later  becomes  irregularly  lobed  and  branching.  Such 
old  colonies  are  often  large  enough  to  be  observed  with 
the  naked  eye.     They  are  found  most  commonly  in  late 

summer,  being  hot 
weather  forms.  When 
abundant  these  two  are 
often  tossed  by  the 
waves  upon  rocks  along 
the  water's  edge,  and 
from  them  the  dirty  blue- 
green  deposit  that  is 
popularly  known  as 
"green  paint." 

Among  the  members 
of  this  group  most  com- 
monly seen  are  the  motile 
blue-greens  of  the  genus 
Oscillatoria  (fig.  5 1 G) . 
These  grow  in  dense,  strongly  colored  tufts  and  patches 
of  exceedingly  slender  filaments  attached  to  the  bottoms 
and  sides  of  watering  troughs,  ditches  and  pools, 
and  on  the  beds  of  ponds  however  stagnant.  They 
thickly  cover  patches  of  the  black  mud  bottom 
and  the  formation  of  gases  beneath  them  disrupts  their 
attachment  and  the  broken  flakes  of  bottom  slime  that 
they  hold  together,  rise  to  the  surface  and  float  there, 
much  to  the  hurt  of  the  appearance  of  the  water. 

The  filaments  of  Oscillatoria  and  of  a  few  of  its  near 
allies  perform  curious  oscillating  and  gliding  movements. 
Detached  filaments  float  freely  in  the  open  water,  and 


Fig.  51.  Miscellaneous  blue-green 
algas  (mostly  after  West). 

A,  Microcystis  (Clathrocystis) ;  B,  C,  D, 
Tetrapedia;  E,  Spirulina;  F,  Nostoc;  G, 
Oscillatoria;    H,  Rivularia. 


134 


Aquatic  Organisms 


during  the  warmer  portion  of  the  year,  are  among  the 
commoner  constituents  of  the  plancton. 

There  are  a  number  of  filamentous  blue-greens  that 
are  more  permanently  sessile,  and  whose  colonies  of 
filaments  assume  more  definite  form.  Rivularia  is 
typical  of  these.  Rivuhiria  grows  in  hemispherical 
gelatinous  lumps,  attached  to  the  leaves  and  stems  of 
submerged  seed  plants.  In  autumn  it  often  fairly 
smothers  the  beds  of  hornwort  (Ceratophyllum)  and 
water   fern    (Marsilea)    in   rich    shoals.     Rivularia   is 


Fig. 


Colonies  of  Rivularia  on  a  disintegrating 
Typha  leaf. 


brownish  in  color,  appearing  dirty  yellowish  under  the 
microscope.  Its  tapering  filaments  are  closely  massed 
together  in  the  center  of  the  rather  solid  gelatinous 
lump.  The  differentiation  of  cells  in  the  single  filament 
is  shown  in  fig.  51//.  Such  filaments  are  placed  side 
by  side,  their  basal  heterocysts  close  together,  their  tips 
diverging.  As  the  mass  grows  to  a  size  larger  than  a  pea 
it  becomes  softer  in  consistency,  more  loosely  attached 
to  its  support  and  hollow.  Strikingly  different  in  form 
and  habits  is  the  raftlike  Mcrismopccdia  (fig.  53).  It 
is  a  flat  colony  of  shining  blue-green  cells  that  divide  in 
two  planes  at  right  angles  to  each  other,  with  striking 


Red  and  Brown  Algae 


K~>5 


in 


regularity.  These  rafts  of  cells  drift  about  freeh 
open  water,  and  are  often  taken  in  the  plancton,  though 
rarely  in  great  abundance.  They  settle  betimes  on  the 
leaves  of  the  larger  water  plants,  and  may  be  discovered 
with  a  pocket  lens  by  searching  the  sediment  shaken 
therefrom. 


Fig.  53.     Merismopaedia. 

Red  and  brown  alg,e  (Rhodophycece  and Phceophycea) 

— These  groups  are  almost  exclusively  marine.  A  few 
scattering  forms  that  grow  in  fresh  water  are  shown  in 
figure  54.  Lemanea  is  a  torrent -inhabiting  form  that 
grows  in  blackish  green  tufts  of  slender  filaments, 
attached  to  the  rocks  in  deep  clear  mountain  streams 
where  the  force  of  the  water  is  greatest.     It  is  easily 


136 


Aquatic  Organisms 


recognizable  by  the  swollen  or  nodulose  appearance  of 
the  ultimate  (fruiting)  branches.  Chantransia  is  a 
beautiful  purplish-brown,  extensively  branching  form 
that  is  more  widely  distributed.  It  is  common  in  clear 
fl<  wing  streams.  It  much  resembles  Cladophorain  man- 
ner of  growth  but  is  at  once  distinguished  by  its  color. 


FlG.  54.     Red  and  brown  algae  (after  West). 
a,  Lemanea;    b,  Chantransia;    c.  Batrachospermum;    d,  Hydrurus. 

Batrachospermum  is  a  freshwater  form  of  wide  distri- 
bution, with  a  preference  for  spring  brooks,  though  occur- 
ring in  any  water  that  is  not  stagnant.  It  grows  in 
branching  filaments  often  several  inches  long,  enveloped 
in  a  thick  coat  of  soft  transparent  mucus.  The  color  is 
bluish  or  yellowish-green,  dirty  yellow  or  brownish. 
Attached  to  some  stick  or  stone  in  a  rivulet  its  sprays,  of 
more  than  frond-like  delicacy,  float  freely  in  the  water. 

Hydrurus  grows  in  branched  colonies  embedded  in  a 
tough  mucilage,  attached  to  rocks  in  cold  mountain 
streams.  The  colonies  are  often  several  inches  long. 
Their  color  is  olive  green.  They  have  a  plumose 
appearance,  and  are  of  very  graceful  outline. 


The  Stoneworts 


137 


The  stoneworts  (Characece) . — This  group  is  well  repre- 
sented in  freshwater  by  two  common  genera,  well  known 
to  every  biological  laboratory  student,  Char  a  and 
Nitella.  Both  grow  in  protected  shoals,  and  in  the 
borders  of  clear  lakes  at  depths  below  the  heavy  beating 
of  the  waves.     Both  are  brittle  and  cannot  withstand 


i?3m 

iyfo 

W&7 

ill 

I  t^lli 

sv' 

Wk    Jfi^^Sf%AI*Pyfi 

hI^blM  ■'11  \Wmii/ 

■x  m 

■^^lSSm^^t 

H 

MjHJ^MM&SjJr 

llH    iPr^l 

Ss**f V 

^sj 

KT 

Fig.  55.     Nitella  glomerulifera. 

wave  action.  Both  prefer  the  waters  that  flow  off  from 
calcareous  soils,  and  are  oftenest  found  attached  to  a 
stony  bottom. 

The  stoneworts,  are  the  most  specialized  of  the  fresh- 
water algae:  indeed,  they  are  not  ranked  as  algae  by 
some  botanists.  In  form  they  have  more  likeness  to 
certain  land  plants  than  to  any  of  the  other  algae. 


138  Aquatic  Organisms 


They  grow  attached  to  the  soil.  They  grow  to  consider- 
able size,  often  a  foot  or  more  in  length  of  stem.  They 
grow  by  apical  buds,  and  they  send  out  branches  in 
regular  whorls,  which  branch  and  branch  again,  giving 
the  plant  as  a  whole  a  bushy  form.  The  perfect  regu- 
larity of  the  whorled  branches  and  the  brilliant  colora- 
tion Of  the  little  spermaries  borne  thereon,  doubtless 
have  suggested  the  German  name  for  them  of  ''Cande- 
labra plants." 

The  stoneworts  are  so  unique  in  structure  and  in  repro- 
ductive parts  that  they  are  easily  distinguished  from 
other  plants.  The  stems  are  made  up  of  nodes  and 
internodes.  The  nodes  are  made  up  of  short  cells  from 
which  the  branches  arise.  The  internodes  are  made  up 
of  long  cells  (sometimes  an  inch  or  more  long),  the 
central  one  of  which  reaches  from  one  node  to  another. 
In  Nitella  there  is  a  single  naked  internodal  cell  com- 
posing entirely  that  portion  of  the  stem.  In  Chara  this 
axial  cell  is  covered  externally  by  a  single  layer  of 
slenderer  cortical  cells  wound  spirally  about  the  central 
one.  A  glance  with  a  pocket  lens  will  determine  whether 
there  is  a  cortical  layer  covering  the  axial  internodal 
cell,  and  so  will  distinguish  Chara  from  Nitella.  Chara 
is  usually  much  more  heavily  incrusted  with  lime  in  our 
commoner  species,  and  in  one  very  common  one,  Chara 
fcctida,  exhales  a  bad  odor  of  sulphurous  compounds. 

The  sex  organs  are  borne  at  the  bases  of  branchlets. 
There  is  a  single  egg  in  each  ovary,  charged  with  a  rich 
store  of  food  products,  and  covered  by  a  spirally  wound 
cortical  layer  of  protecting  cells.  These,  when  the  egg 
is  fertilized  form  a  hard  shell  which,  like  the  coats  of  a 
seed,  resist  unfavorable  influences  for  a  long  time. 
This  fruit  ripens  and  falls  from  the  stem.  It  drifts 
about  over  the  bottom,  and  later  it  germinates. 

At  the  apex  of  the  ovary  is  a  little  crown  of  cells, 
between  which  lies  the  passageway  for  the  entrance  of 


Chlorophylless  Plants  139 


the  sperm  cell  at  the  time  of  fertilization.  This  crown 
is  composed  of  five  cells  in  Chara;  of  ten  cells  in  Nitella. 
It  is  deciduous  in  Chara;   it  is  persistent  in  Nitella. 

The  stoneworts,  unlike  many  other  algae,  are  wonder- 
fully constant  in  their  localities  and  distribution,  and 
regular  in  their  season  of  fruiting.  They  cover  the 
same  hard  bottoms  with  the  same  sort  of  gray -green 
meadows,  year  after  year,  and  although  little  eaten  by 
aquatic  animals,  they  contribute  important  shelter  for 
them,  and  they  furnish  admirable  support  for  many 
lesser  epiphytes. 

CHLOROPHYLLESS  WATER  PLANTS,  BACTERIA 
AND  FUNGI 

Nature's  great  agencies  for  the  dissolution  of  dead 
organic  materials,  in  water  as  on  land,  are  the  plants 
that  lack  chlorophyl.  They  mostly  reproduce  by 
means  of  spores  that  are  excessively  minute  and  abund- 
ant, and  that  are  distributed  by  wind  or  water  every- 
where; consequently  they  are  the  most  ubiquitous  of 
organisms.  They  consume  oxygen  and  give  off  carbon 
dioxide  as  do  the  animals,  and  having  no  means  of 
obtaining  carbon  from  the  air,  must  get  it  from  car- 
bonaceous organic  products — usually  from  some  carbo- 
hydrate, like  sugar,  starch,  or  cellulose.  Some  of  them 
can  utilize  the  nitrogen  supply  of  the  atmosphere  but 
most  of  them  must  get  nitrogen  also  from  the  decompo- 
sition products  of  pre-existing  proteins.  Many  of  them 
produce  active  ferments,  which  expedite  enormously  the 
dissolution  of  the  bodies  of  dead  plants  and  animals. 
Some  bacteria  live  without  free  oxygen. 

It  follows  from  the  nature  of  their  foods,  that  we  find 
these  chlorophylless  plants  abounding  where  there  is  the 
best  supply  of  organic  food  stuffs:  stagnant  pools 
filled  with  organic  remains,  and  sewers  laden  with  the 


140  Aquatic  Organisms 

city's  waste.  But  there  is  no  natural  water  free  from 
tli cm.  Let  a  dead  fly  fall  upon  the  surface  of  a  tumbler 
of  pond  water  and  remain  there  for  a  day  or  two  and  it 
becomes  white  with  water  mold,  whose  spores  were 
present  in  the  water.  Let  any  organic  solution  stand 
exposed  and  quickly  the  evidence  of  rapid  decomposition 
appears  in  it.  Even  the  dilute  solutions  contained  in  a 
laboratory  aquarium,  holding  no  organic  material  other 
than  a  few  dead  leaves  will  often  times  acquire  a  faint 
purple  or  roseate  hue  as  chromogenic  bacteria  multiply 
in  them. 

Bacteria — A  handful  of  hay  in  water  will  in  a  few 
hours  make  an  infusion,  on  the  surface  of  which  a  film 
of  "bacterial  jelly"  will  gather.  If  a  bit  of  this  "jelly" 
be  mounted  for  the  microscope,  the  bacteria  that  secrete 
it  may  be  found  immersed  in  it,  and  other  bacteria 
will  be  found  adherent  to  it.  All  the  common  form- 
types,  bacillus,  coccus  and  spirillum  are  likely  to  be  seen 
readily.  Thus  easy  is  it  to  encourage  a  rich  growth  of 
water  bacteria.  Among  the  bacteria  of  the  water  are 
numerous  species  that  remain  there  constantly  (often 
called  "natural  water  bacteria"),  commingled  at  certain 
times  and  places  with  other  bacteria  washed  in  from  the 
surface  of  the  soil,  or  poured  in  with  sewage.  From  the 
last  named  source  come  the  species  injurious  to  human 
health.  These  survive  in  the  open  water  for  but  a  short 
time.  The  natural  water  bacteria  are  mainly  beneficial ; 
they  assist  in  keeping  the  world's  food  supply  in  circula- 
tion. Certain  of  them  begin  the  work  of  altering  the 
complex  organic  substances.  They  attack  the  proteins 
and  produce  from  them  ammonia  and  various  ammonia- 
cal  compounds.  Then  other  bacteria,  the  so-called 
"nitrifying"  bacteria  attack  the  ammonia,  changing  it 
to  simpler  compounds.  Two  kinds  of  bacteria  succes- 
sively   participate    in    this:     one    kind    oxidizes    the 


Bacteria  141 


ammonia  to  nitrites;  a  second  kind  oxidizes  the 
nitrites  to  nitrates.  By  these  successive  operations  the 
stores  of  nitrogen  that  are  gathered  together  within  the 
living  bodies  of  plants  and  animals  are  again  released 
for  further  use.  The  simple  nitrates  are  proper  food 
for  the  green  algae,  with  whose  growth  the  cycle  begins 
again.  And  those  bacteria  which  promote  the  pro- 
cesses of  putrefaction,  are  thus  the  world's  chief  agen- 
cies for  maintaining  undiminished  growth  in  perpetual 
succession. 

Bacteria  are  among  the  smallest  of  organisms.  Little 
of  bodily  structure  is  discoverable  in  them  even  with 
high  powers  of  the  microscope,  and  consequently  they 
are  studied  almost  entirely  in  specially  prepared  cul- 
tures, made  by  methods  that  require  the  technical 
training  of  the  bacteriological  laboratory  for  their 
mastery.  Any  one  can  find  bacteria  in  the  water,  but 
only  a  trained  specialist  can  tell  what  sort  of  bacteria 
he  has  found;  whether  pathogenic  species  like  the 
typhoid  bacillus,  or  the  cholera  spirillum;  or  whether 
harmless  species,  normal  to  pure  water. 

The  higher  bacteria — Allied  to  those  bacilli  that  grow 
in  filaments  are  some  forms  of  larger  growth,  known  as 
Trichobacteria,  whose  filaments  sometimes  grow 
attached  in  colonies,  and  in  some  are  free  and  motile. 
A  few  of  those  that  are  of  interest  and  importance  in 
fresh-water  will  be  briefly  mentioned  and  illustrated 
here. 

Leptothrix*  (Fig.  56a,  b  and  c)  grows  in  tufts  of  slender, 
hairlike  filaments  composed  of  cylindric  cells  sur- 
rounded by  a  thin  gelatinous  sheath.  In  reproduction 
the  cells  are  transformed  directly  into  spores  (gonidia) 
which  escape  from  the  end  of  the  sheath  and,  finding 
favoring  conditions,  grow  up  into  new  filaments. 

*Known  also  as  Streptothrix  and  Chlamydothrix. 


142 


Aquatic   Organisms 


Crenothrix  (Fig.  56  d,  e  and/)  is  a  similar  unbranched 
sessile  form  which  is  distinguished  by  a  widening  of  the 
filaments  toward  the  free  end.  This  is  caused  by  a 
division  of  the  cells  in  two  or  three  planes  within  the 
sheath  of  the  filament,  previous  to  spore  formation. 
Often  by  the  germination  of  spores  that  have  settled 
upon  the  outside  of  the  old  sheaths  and  growth  of  new 
filaments  therefrom  compound  masses  of  appreciable 


Fig. 


Trichobacteria. 


a,  b,  c,  Leptothrix  (Slreptothrix,  or  Chlamydothrix).  a,  a  colony;  b,  a  single  filament;  c,  spore 
formation;  d,  e,  /,  Crenothrix;  d,  a  single  growing  filament;  e,  a  fruiting  filament;  /,  a 
compound  colony;  g,  Cladothrix,  a  branching  filament;  h,  Beggiatoa,  younger  and  older 
filaments,  the  latter  showing  sulphur  granules,  and  no  septa  between  cells  of  the  filament. 


size  are  produced.  In  the  sheaths  of  the  filaments  a 
hydroxide  of  iron  is  deposited  (for  Crenothrix  possesses 
the  power  of  oxidizing  certain  forms  of  iron) ;  and  with 
continued  growth  the  deposits  sometimes  become 
sufficient  to  make  trouble  in  city  water  supply  systems 
by  stoppage  of  the  pipes.  In  nature,  also,  certain 
deposits  of  iron  are  due  to  this  and  allied  forms  properly 
known  as  iron  bacteria.  Cladothrix  (Fig.  56  g),  is  a 
related  form  that  exhibits  a  peculiar  type  of  branching 
in  its  slender  cylindric  filaments. 


Water  Molds 


143 


Beggiatoa  (fig.  56  h)  is  the  commonest  of  the  so-called 
sulfur  bacteria.  Its  cylindric  unbranched  and  unat- 
tached filaments  are  motile,  and  rotate  on  the  long  axis 
with  swinging  of  the  free  ends.  The  boundaries  be- 
tween the  short  cylindric  cells  are  often  obscure, 
especially  when  (as  is  often  the  case)  the  cells  are  filled 
with  highly  refractive  granules  of  sulfur.  Considerable 
deposits  of  sulfur,  especially  about  springs,  are  due  to 
the  activities  of  this  and  allied  forms. 

Water  molds — True  fungi  of  a  larger  growth  abound 
in  all  fresh  waters,  feeding  on  almost  every  sort  of 
organic  substance  contained 
therein.  The  commonest  of 
the  water  molds  are  the  Sap- 
rolegnias,  that  so  quickly 
overgrow  any  bit  of  dead 
animal  tissue  which  may 
chance  to  fall  upon  the  sur- 
face of  the  water  and  float 
there.  If  it  be  a  fly,  in  a 
day  or  two  its  body  is  sur- 
rounded by  a  white  fringe  of 
radiating  fungus  filaments, 
outgrowing  from  the  body. 
The  tips  of  many  of  these 
filaments  terminate  in  cylin- 
dric sporangia,  which  when 


Fig.  57.  A  common  water  mold, 
Saprolegnia.  (After  Engler  and 
Prantl.) 

a,  a  colony  growing  on  a  dead  fly;  b,  a  bit 
of  the  mycelium  that  penetrates  the 
fly's  body ;  c.  a  fruiting  tip,  with  escap- 
ing swarm  spores. 


mature,  liberate  from  their  ruptured  tips  innumerable 
biciliated  free-swimming  swarm  spores.  These  wander 
in  search  of  new  floating  carcases,  or  other  suitable  food. 
Certain  of  these  water  molds  attack  living  fishes, 
entering  their  skin  wherever  there  is  a  a  slight  abrasion 
of  the  surface,  and  rapidly  producing  diseased  condi- 
tions. These  are  among  the  worst  pests  with  which  the 
fish  culturist  has  to  contend.     Thev  attack  also  the 


144  Aquatic  Organisms 


eggs  of  fishes  during  their  incubation,  as  shown  in  a 
figure  in  a  later  chapter. 

Most  water  molds  live  upon  other  plants.  Even  the 
Saprolegnias  have  their  own  lesser  mold  parasites. 
Many  living  algae,  even  the  lesser  forms  like  desmids 
and  diatoms  are  subject  to  their  attack.  Fine  cultures 
of  such  algae  are  sometimes  run  through  with  an 
epidemic  of  mould  parasites  and  ruined. 


THE    HIGHER    PLANTS 
(Mossworts,    Femworts  and  Seed  Plants) 

In  striking  contrast  with  the  algae,  the  higher  plants 
live  mainly  on  land,  and  the  aquatics  among  them 
are  restricted  in  distribution  to  shoal  waters  and  to 
the  vicinity  of  shores.  There  is  much  in  the  bodily 
organization  of  nearly  all  of 
them  that  indicates  ancestral 
adaptation  to  life  on  land. 
They  have  more  of  hard  parts, 
more  of  localized  feeding 
organs,  more  of  epidermal 
specialization,  and  more  dif- 
erentiation  of  parts  in  the 
body,  than  life  in  the  water 
demands. 

They  occupy  merely  the 
margins  of  the  water.  A  few 
highly  specialized  genera, 
well  equipped  for  with- 
standing partial  or  complete 
submergence  occupy  the 
shoals  and  these  are  backed 
on  the  shore  line  by  a 
mingled  lot  of  semi-aquatics  that  are  for  the  most  part 
but  stray  members  of  groups  that  abound  on  land. 
Often  they  are  single  members  of  large  groups  and  are 
sufficiently  distinguished  from  their  fellows  by  a  name 
indicating  the  kind  of  wet  place  in  which  they  grow. 
Thus  we  know  familiarly  the  floating  riccia,  the  bog 
mosses,  the  brook  speedwell,  the  water  fern  and  water 
cress,  the  marsh  bell  flower  and  the  marsh  fern,  the 
swamp  horsetail  and  the  swamp  iris,  etc.     All  these 

145 


Fig.    58.     The    marsh    mallow, 
Hibiscus  Moscheutos. 


1^.6  Aquatic  Organisms 

and  many  others  are  stragglers  from  large  dry  land 
groups.  That  readaptation  to  aquatic  life  has  occurred 
many  times  independently  is  indicated  by  the  fact  that 
the  more  truly  aquatic  families  are  small  and  highly 
specialized,  and  are  widely  separated  systematically. 

Bryophytcs — Both  liverworts  and  mosses  are  found 
in  our  inland  waters,  though  the  former  are  but  spar- 
ingly represented.  Two  simple  Riccias,  half  an  inch  long 
when  grown,  are  the  liverworts  most  commonly  found. 
One,  Ricciafluitans,  grows  in  loose  clusters  of  flat  slender 
forking  sprays  that  drift  about  so  freely  that  fragments 
are  often  taken  in  pond  and  river  plancton.  The  larger 
unbroken  more  or  less  spherical  masses  of  sprays  are  found 
rolling  with  the  waves  upon  the  shores  of  muddy  ponds. 
The  other,  Ricciocarpus  natans,  has  larger  and  thicker 
sprays  of  green  and  purple  hue,  that  float  singly  upon  the 
surface,  or  gather  in  floating  masses  covering  considerable 
areas  of  quiet  water.  They  are  not  uncommonly  found  in 
springtime  about  the  edges  of  muddy  ponds.  Under- 
neath the  flat  plant  body  there  is  a  dense  brush  of 
flattened  scales. 

Water  mosses  are  more  important.  The  most 
remarkable  of  these  are  the  bog  mosses  {Sphagnum). 
These  cover  large  areas  of  the  earth's  surface,  especially 
in  northern  regions,  where  they  chiefly  compose  the 
thick  soft  carpet  of  vegetation  that  overspreads  open 
bogs  and  coniferous  swamps.  They  are  of  a  light  grey- 
green  color,  often  red  or  pink  at  the  tips.  These 
mosses  do  not  grow  submerged,  but  they  hold  immense 
quantities  of  water  in  their  reservoir  cells,  and  are  able 
to  absorb  water  readily  from  a  moist  atmosphere ;  so 
they  are  always  wet.  Supported  on  a  framework  of 
entangled  rootstocks  of  other  higher  plants,  the  bog 
mosses  extend  out  over  the  edges  of  ponds  in  floating 
mats,  which  sink  under  one's  weight  beneath  the  water 


Moss-worts 


H; 


level  and  rise  again  when  the  weight  is  removed.  The 
part  of  the  mat  which  the  sphagnum  composes  consists 
of  erect,  closely-placed,  unbranched  stems,  like  those 
shown  in  fig.  59,  which  grow  ever  upward  at  their  tips, 


Fig.  59.     Bog  moss,  Sphagnum. 


and  die  at  the  lower  ends,  contributing  their  remains 
to  the  formation  of  beds  of  peat. 

The  leaves  of  Sphagnum  are  composed  of  a  single  layer 
of  cells  that  are  of  two  very  different  sorts.  There  are 
numerous  ordinary  narrow  chlorophyl-bearing  cells,  and, 
lying  between  these,  there  are  larger  perforate  reservoir 
cells,  for  holding  water. 


i48 


Aquatic    Groan  isms 


The  true  water  mosses  of  the  genus  Fontinalis  are 
fine  aquatic  bryophytes.  These  are  easily  recognized, 
being  very  dark  in  color  and  very  slender.  They  grow 
in  spring  brooks  and  in  clear  streams,  and  are  often  seen 
in  great  dark  masses  trailing  their  wiry  stems  where  the 
current  rushes  between  great  boulders  or  leaps  into 
foam-flecked  pools  in  mountain  brooks. 

Another  slender  brook-inhabiting  moss  is  Fissidens 
julia  n  urn,  which  somewhat  resembles  Fontinalis,  but 
which  is  at  once  distinguished  by  the  deeply  channeled 

bases  of  its  leaves,  which 
enfold  the  stem.  The 
leaves  are  two  ranked  and 
alternate  along  the  very 
slender  flexuous  stem,  and 
appear  to  be  set  with  edges 
toward  it. 

There  are  also  a  few 
lesser  water  mosses  allied 
to  the  familiar  trailing 
hypnums,  so  common  in 
deep  woods.  They  grow 
on  stones  in  the  bed  of 
brooks.  They  cover  the 
face  of  the  ledges  over 
which  the  water  pours  in 
floods  and  trickles  in  times  of  drouth,  as  with  a  fine 
feathery  carpet  of  verdure  that  adds  much  to  the  beauty 
of  the  little  waterfalls.  They  give  shelter  in  such  places 
to  an  interesting  population  of  amphibious  animals,  as 
will  be  noted  in  chapter  VI,  following.  The  leaves  of  the 
hvpnums  are  rather  short  and  broad,  and  in  color  they 
are  often  very  dark — often  almost  black.* 


Fig.  60.     Water  mosses. 

,  Fontinalis;  b,  Fissidens  julianum,  with  a 
single  detached  leaf,  more  enlarged;  c, 
Rhvnchostegium  rusciforme,  with  a  single 
detached  leaf  at  the  left.     (After  Grout.) 


*Grout  has  given  a  few  hints  for  the  recognition  of  these  "Water-loving 
hvpnums"  in  his  Mosses  with  <i  Hand  Lens,  26.  edition,  p.  128.  New  York, 
I905- 


Peteridophytes 


149 


There  are  also  a  few  hypnums  found  intermixed  with 
sphagnum  on  the  surface  of  bogs,  and  as  everyone 
knows  there  are  hosts  of  mosses  in  all  moist  places  in 
woods  and  by  watersides. 


Fig.  61.     Two  floating  leaves  of  the  "water  shamrock,"  Marsilea,  in  the  midst 
of  a  surface  layer  of  duck-meat  (Spirodela  polyrhiza).     "Lemna"  on  fig.  62. 

Pteridophytes — Aquatic  fernworts  are  few  and  of  very 
unusual  types.  There  is  at  least  one  of  them,  how- 
ever, that  is  locally  dominant  in  our  flora.  Marsilea, 
the  so-called  water  shamrock  or  water  fern,  abounds.  >n 


150 


Aquatic  Organisms 


the  sunny  shoals  of  muddy  bayous  about  Ithaca  and  in 
many  places  in  New  England.  It  covers  the  zone 
between  high  and  low  water,  creeping  extensively  over 
the  banks  that  are  mostly  exposed,  and  there  forming 
a  most  beautiful  ground  cover,  while  producing  longer 
leaf -stalks  where  submerged.  These  leaf -stalks  carry 
the  beautiful  four-parted  leaf-blades  to  the  surface 
where  they  float  graceful!}'.     Fruiting  bodies  the  size 


Fig.  62.     Floating  plants:     The  largest  branching  colonies  are  Azolla;    the 
smallest  plants  are  Wolfiia;    those  of  intermediate  size  are  Lemna  minor. 

l'huto  by  Dr.  Emmeline  Moure. 


of  peas  are  produced  in  clusters  on  the  creeping  stems 
above  the  water  line,  often  in  very  great  abundance. 

Then  there  are  two  floating  pteridophytes  of  much 
interest.  Salvia  ia,  introduced  from  Europe,  is  found 
locally  along  our  northeastern  coast,  and  in  the  waters 
of  our  rich  interior  bottom  lands  the  brilliant  little 
Azolla  flourishes.  Azolla  floats  in  sheltered  bogs 
and  back  waters,  intermingled  with  duckweeds.  It  is 
reddish  in  color  oftener  than  green  and  grows  in  minute 
mosslike    pinnately    branched    sprays,    covered    with 


Aquatic  Seed  Plants  151 

closely  overlapping  two-lobed  leaves,  and  emits  a  few 
rootlets  from  the  under  side  which  hang  free  in  the 
water.  In  the  back  waters  about  the  Illinois  Station  at 
Havana,  Illinois,  Azolla  forms  floating  masses  often 
several  feet  in  diameter,  of  bright  red  rosettes. 

Shoreward  there  are  numerous  pteridophytes  grow- 
ing as  rooted  and  emergent  aquatics ;  the  almost  grass- 
like Isoetes,  and  the  marsh  horsetails  and  ferns,  but 
these  latter  differ  little  from  their  near  relatives  that 
live  on  land. 

Aquatic  Seed  Plants — These  are  manifestly  land 
plants  in  origin.  They  have  much  stiffening  in  their 
stems.  They  have  a  highly  developed  epidermal 
system,  often  retaining  stomates,  although  these  can 
be  no  longer  of  service  for  intake  of  air.  They  effect 
fertilization  by  means  of  sperm  nuclei  and  pollen  tubes, 
and  not  by  free  swimming  sperm  cells. 

Seed  plants  crowd  the  shore  line,  but  they  rapidly 
diminish  in  numbers  in  deepening  water.  They  grow 
thickest  by  the  waterside  because  of  the  abundance  of 
air  moisture  and  light  there  available.  But  too  much 
moisture  excludes  the  air  and  fewer  of  them  are  able  to 
grow  where  the  soil  is  always  saturated.  Still  fewer 
grow  in  standing  water  and  only  a  very  few  can  grow 
wholly  submerged.  Moreover,  it  is  only  in  protected 
shoals  that  aquatic  seed  plants  flourish.  They  cannot 
withstand  the  beating  of  the  waves  on  exposed  shores. 
Their  bodies  are  too  highly  organized,  with  too  great 
differentiation  of  parts.  Hence  the  vast  expanses  of 
open  waters  are  left  in  possession  of  the  more  simply 
organized  algae. 

An  examination  of  any  local  flora,  such  as  that  of 
the  Cayuga  Lake  Basin*  will  reveal  at  once  how  small  a 
part  of  the  population  is  adapted  for  living  in  water. 

*The  following  data  are  largely  drawn  from  Dudley's  Cayuga  Flora,  1886. 


152 


Aquatic  Organisms 


In  this  area  there  are  recorded  as  growing  without 
cultivation  1278  species.  Of  these  392  grow  in  the 
water.  However,  fewer  than  forty  species  grow  wholly 
submerged,  with  ten  or  a  dozen  additional  submerged 
exc<  -pt  for  floating  leaves.     Hardly  more  than  an  eighth, 

therefore,  of  the  so- 
called  "aquatics"  are 
truly  aquatic  in  mode 
of  life:  the  remaining 
seven-eighths  grow  on 
shores  and  in  springs, 
in  swamps  and  bogs,  in 
ditches,  pools,  etc., 
where  only  their  roots 
are  constantly  wet. 

The  aquatic  seed 
plants  are  representa- 
tive of  a  few  small  and 
scattered  families.  In- 
deed, the  only  genus 
having  any  consider- 
able number  of  truly 
aquatic  species  is  the 
naiad  genus  Potamo- 
geton.  Other  genera 
of  river- weeds,  or  true 
pond  weeds,  are  small, 
scattered  and  highly 
diversified.  They  bear 
many  earmarks  of 
the  special  situations 
In  the 


Fig.  63.  The  ruffled  pond-weed;  Pota- 
mogeton  crispits,  one  of  the  most  orna- 
mental of  fresh  water  plants. 


independent  adaptation  to 
in  the  water  which  they  severally  occupy 
economy  of  nature  the  Potamogetons  or  river  weeds 
constitute  the  most  important  single  group  of  sub- 
merged seed  plants.  They  are  rooted  to  the  bottom 
in  most  shoal  waters,  and  compose  the  greater  part  of 


Aquatic  Seed  Plants  153 

the  larger  water  meadows  within  our  flora.  They  have 
alternate  leaves  and  slender  flexuous  stems  that  are 
often  incrusted  with  lime. 

There  are  evergreen  species  among  the  Potamogetons . 
and  other  species  that  die  down  in  late  summer.  Thei  e 
are  broad  leaved  and  narrow  leaved  species.  There 
are  a  few,  like  the  familiar  Potamogeton  natans  whose 
uppermost  leaves  float  flat  upon  the  surface,  but 
the  more  important  members  of  the  genus  live  wholly 
submerged.  Tho  seed-plants,  they  mainly  reproduce 
vegetatively,  by  specialized  reproductive  buds  that  are 
developed  in  the  growing  season,  and  are  equipped  with 
stored  starch  and  other  food  reserves,  fitting  them  when 
detached  for  rapid  growth  in  new  situations.  These 
reproductive  parts  are  developed  in  some  species  as 
tuberous  thickenings  of  underground  parts;  in  others 
as  burr-like  clusters  of  thickened  apical  buds ;  and  in 
still  others  they  are  mere  thickenings  of  detachable 
twigs. 

The  Potamogetons  enter  largely  into  the  diet  of  wild 
ducks  and  aquatic  rodents  and  other  lesser  aquatic 
herbivores.  They  are  as  important  for  forage  in  the 
water  as  grasses  are  on  land. 

Other  naiads  are  Nats  (fig.  85)  and  Zannichellia. 

Eel-grass  {Vallisneria)  is  commonly  mixed  with  the 
pond  weeds  in  lake  borders  and  water  meadows. 
Eel-grass  is  apparently  stemless  and  has  long,  flat, 
flexuous,  translucent,  ribbonlike  leaves,  by  which  it 
is  easily  recognized.  The  duckweeds  (Lemnaceae,  figs. 
61  and  62)  are  peculiar  free-floating  forms  in  which  the 
plant  body  is  a  small  flat  thallus,  that  drifts  about  freely 
on  the  surface  in  sheltered  coves,  mingled  with  such 
liverworts  as  Ricciocarpus,  with  such  fernworts  as 
Azolla,  with  seeds,  eel-grass  flowers,  and  other  flotsam 
There  are  definite  upper  and  lower  surfaces  to  the  thal- 
lus with  pendant  roots  beneath  hanging  free  in  the 


154 


qiidtic  Organisms 


water.  Increase  is  by  budding  and  outgrowth  of  new 
lobes  from  pre-existing  thalli.  Flowering  and  seed 
production  are  of  rare  occurrence. 

The  water  lily 
family  includes 
the  more  con- 
spicuous of  the 
broad- leaved 
aquatics,  which 
pre-empt  the 
rich  bottom  mud 
with  stout  root 
stocks,  and 
heavily  shade 
the  water  with 
large  shield- 
shaped  leaves, 
either  floating 
upon  the  sur- 
face, as  in  the 
water  shield  and 
water  lilies  or 
lifted  somewhat 
above  it,  as  in  the 
spatterdock  and 
the  lotus.  They 
are  long-lived 
perennials,  re- 
quiring a  rich 
muck  soil  to  root 
in.     These  are 

Fig.  64.     Leaf- whorls.  distinguished 

.4,  and  f,  the  hornwort  (f?rflfo/)/fr//Hm);    B,  the  water  nilfoil  for      the     beailtV 

(Myriophyllum).     A  is  an  old  leaf,  the  upper  half  normally  1 

covered  with  algae  and  silt;   the  lower  half  cleaned,  save  for  a  ailQ  ira°TanCe  Of 

closely  adherent  dwelling-tube  of  a  midge  larva  in  the  fork  at  1       •      _n 

the  right.     C.  is  a  young  partly  expanded  leaf  whorl  from  the  their  flOWCrS 
apical  bud. 


Aquatic   Seed  Plants 


oo 


The  bladderworts  (Utricularia)  comprise  another 
peculiar  group.  They  are  free-floating,  submerged 
plants  with  long,  flexuous  branching  stems  that  are 
thickly  clothed  with  dissected  leaves.  Attached  to  the 
leaves  are  the  curious  traps  or  "bladders"  (discussed  in 
Chapt.  VI)  which  have  suggested  the  group  name. 
Being  unattached  they  frequent  the  still  waters  of 
sheltered  bays  and  ponds  where  they  form  beautiful 
feathery  masses  of  green.  They  shoot  up  stalks  above 
the  surface  bearing  curious  bilabiate  flowers. 


Fig.  65.  The  water  weed,  Philotria  (Anacharis  or  Elodea),  with 
two  young  black-and-green-banded  nymphs  of  the  dragonfly  A  mix 
on  its  stem,  and  a  snail,  Planorbis,  on  a  leaf. 

The  hornwort  (Ceratophyttum)  is  another  non-rooting 
water  plant  that  grows  wholly  submerged  and  branch- 
ing. It  is  coarser,  however,  and  hardier  than  Utricu- 
laria and  much  more  widespread.  Its  leaves  are  stiff, 
repeatedly  forking,  and  spinous-tipped  (fig.  64  A  and  C). 

The  water  milfoils  (Myriophyllum)  are  rooted  aqua- 
tics, superficially  similar  to  the  hornwort  but  dis- 
tinguishable at  a  glance  by  the  simple  pinnate  branch- 
ing of  the  softer  leaves  (fig.  64^). 

Then  there  are  a  few  very  common  aquatics  that 
form  patches  covering  the  beds  of  lesser  ponds,  bogs 


I.S6 


Aquatic  Organisms 


and  pools.  The  common  water  weed,  Ph  Hot r in ,  (fig.  65) , 
with  its  neat  little  leaves  regularly  arranged  in  whorls  of 
threes;  and  two  water  crowfoots,  Ranunculus,  (fig.  66), 
white  and  yellow,  with  alternate  finely  dissected  leaves ; 
and  the  water  purslane,  Ludvigia  palustris,  with  its 
closely-crowded  opposite  ovate  leaves  are  found  here. 
These  are  the  common  plants  of  the  waterbeds  about 
Ithaca.     They  are  so  few  one  may  learn  them  quickly, 

for  so  strongly  marked 
are  they  that  a  single 
spray  or  often  a  single 
leaf  is  adequate  for 
recognition. 

Then  there  are  three 
small  families  so  finely 
adapted  to  withstand- 
ing root  submersion 
that  they  dominate  all 
our  permanent  shoals 
and  marshes.  These 
are  (1)  the  Typhaceae 
including  the  cat -tails 
and  the  bur-reeds, 
which  form  vast  stretch- 
es  of  nearly  clear 
growth,  as  discussed  in  the  last  chapter;  (2)  the  Alis- 
maceae,  including  arrow  heads  and  water  plantain,  and 
(3)  the  Pontederiaceae,  represented  by  the  beautiful  blue 
pickerel-weed.  All  these  are  shown  in  their  native 
haunts  in  the  figures  of  chapter  VI. 

Another  family  of  restricted  aquatic  habitat  is  the 
Droseraceae,  the  sun-dews,  which  grow  in  the  borders  of 
sphagnous  upland  bogs.  They  are  minute  purplish- 
tinted  plants  whose  leaves  bear  glandular  hairs. 

Few  other  families  are  represented  in  the  water  by 
more  than  a  small  proportion  of  their  species.     Those 


Fig.  66.     A  leaf  of  the  white  water-crow 
foot,   Ranunculus. 


Aquatic  Seed  Plants 


07 


families  are  best  represented  whose  members  live 
chiefly  on  low  grounds  and  in  moist  soil.  A  few  rushes 
(Juncaceae)  invade  the  water  on  wave-washed  shores 
at  fore  front  of  the  standing  aquatics.      A  few  sedges 


Fig.  67.  Fruit  clusters  of  four  emergent  aquatic  seed 
plants;  arrow-arum  {Peltandra),  pickerel- weed  {Pon- 
tederia),    burr-reed    (Sparganium),    and    sweet    flag 

(A  corns). 

(Carices)  overrun  flood-plains  or  fringe  the  borders  of 
ditches.  A  very  few  grasses  preempt  the  beds  of 
shallow  and  impermanent  pools.  A  few  aroids,  such 
as  arrow  arum  and  the  calla  adorn  the  boggy  shores. 
A  few  heaths,  such  as,  Cassandra  and  Andromeda  over- 
spread the  surface  of  upland  sphagnum  bogs  with  dense 


153 


A q italic  Organisms 


levels  of  shrubs,  and  numerous  orchids  occupy  the  sur- 
face of  the  bog  beneath  and  between  the  shrubs. 
Willows  and  alders  fringe  all  the  streams,  associated 
there  with  a  host  of  representatives  of  other  families 
crowding  down  to  the  waterside.  A  few  of  these  on 
account  of  their  usefulness  or  their  beauty,  we  shall 
have  occasion  to  consider  in  a  subsequent  chapter. 

Such  are  the  dominant  aquatic  seed  plants  in  the 
Cayuga  Basin;  and  very  similar  are  they  over  the 
greater  part  of  the  earth.  The  semi-aquatic  represen- 
tatives of  the  larger  families  are  few  and  differ  little 
from  their  terrestrial  relatives:  the  truly  aquatic 
families  are  small  and  highlv  diversified. 


plants,  so  with  animals,  it 
are  predominantly  aquatic. 


AISI-YALS 

ANY  of  the  lower  groups  of 
animals  are  wholly  aqua- 
tic, never  having  de- 
parted from  their  ances- 
tral abode.  Other  groups 
are  in  part  adapted  to 
life  on  land.  A  few 
others,  after  becoming  fit 
for  terrestrial  life,  have 
been  readapted  in  part  to 
life  in  the  water.  Aqua- 
tic insects  and  mammals, 
especially,  give  evidence 
of  descent  from  terres- 
trial ancestors.  As  with 
is  the  lower  groups  that 


The  simplest  of  animals 


are  the  protozoans;   so  with  these  we  will  begin. 


Protozoans 


159 


Protozoans — One  of  the  best  known  animals  in  the 
world,  one  that  is  pedagogically  exploited  in  every 
biological  laboratory,  is  the  Amoeba  (fig.  69a).  Plastic, 
ever  changing  in  form  and  undifferentiated  in  parts, 
this  is  the  animal  that  is  the  standard  of  comparison 
among  things  primitive.  Its  name 
has  become  a  household  word,  and  an 
every-day  figure  of  speech.  A  little 
living  one-celled  mass  of  naked  pro- 
toplasm, that  creeps  freely  about 
amid  the  ooze  of  the  pond  bottom, 
and  feeds  on  organic  foods.  It 
grows  just  large  enough  to  be  recog- 
nized by  the  naked  eye  when  in  most 
favorable  light,  as  when  creeping  up 
the  side  of  a  culture  jar:  on  the 
pond  bottom  it  is  undiscoverable 
and  a  microscope  is  essential  to 
study  it. 

Related  to  Amoeba  are  several 
common  shell -bearing  forms  of  the 
group  of  Sarcodina  (Rhizopoda) 
that  often  become  locally  abun- 
dant. Difflugia  (fig.  69c)  forms  a 
flask-shaped  shell  composed  of  mi- 
nute granules,  that,  magnified,  look 
like  grains  of  sand  stuck  together 
over  the  outside.  The  soft  amceba-like  body  protrudes 
in  pseudopodia  from  the  mouth  of  the  flask,  when  travel- 
ing or  foraging,  or  withdraws  inside  when  disturbed. 
Arcella  (fig.  69Z?)  secretes  a  broadly  domeshaped  shell, 
having  a  concave  bottom,  in  the  center  of  which  is  the 
hole  whence  dangle  the  clumsy  pseudopodia.  One 
species  of  Arcella,  shown  in  the  following  figure,  has 
the  margin  of  the  shell  strongly  toothed.  Both  of 
these  genera,   and  other  shell-bearing  forms,   secrete 


Fig.  69.     Protozoans. 

a,    Amoeba;    b,  Arcella;    c 
Difflugia. 


i6o 


A  q untie  Organisms 


Fig.  70.  Arcella  dentata. 
Through  the  central  opening 
there  is  seen  a  diatom,  re- 
cently swallowed. 


bubbles  of  gas  within  their 
shells  whereby  they  are  caused 
to  float.  Thus  they  are  often 
taken  in  the  plancton  net  from 
open  water  of  the  ponds  and 
streams. 

Other  protozoans  that  have 
the  body  more  or  less  cov- 
ered with  vibratile  cilia  (Cil- 
iata),  are  very  common  in 
freshwater,  especially  in  ponds 
and  pools.  Best  known  of 
these  is  Paramecium,  (fig. 
71a)  another  familiar  biolog- 
ical-laboratory   "type"     that 

grows  abundantly  in  plant  infusions.     It  is  found  in 

stagnant  pools,   swimming   near   the  surface.     There 

are  many  species  of  Paramecium.     Some  of  them  and 

some  members  of  allied   genera   are   characteristic    of 

polluted    waters.      Other  allied  genera  are  parasitic, 

and  live  within  the  bodies  of  the 

higher  animals.    Stentoris  (as  the 

name    signifies)    a   more    or  less 

trumpet-shaped  ciliate  protozoan, 

that  may  detach  itself  and  swim 

freely   about,   but  that   is   ordi- 
narily   attached    by  its    slender 

base  to  some  support.     Its  base 

is  in  some  species  surrounded  by 

a    soft     gelatinous     transparent 

lorica,  as   shown    in  the  figure. 

Some  species  are  of  a   greenish 

color.    Stentor  and  Paramecium, 

tho   unicellular,  are   quite  large 

enough  to   be   seen   (as   moving 

specks)  with  the  unaided  eye. 


Ciliate  pro- 
tozoans. 


.1,  ParamcBcium;  n,  nu- 
cleus; v,  v,  vacuoles;  /, 
food-ball  at  the  bottom  of 
the  rudimentary  esopha- 
gus; C,  St  en  tor;    I,  lorica. 


Protozoans 


161 


Cothurnia  (fig.  73c)  is  a  curious  double  form  that  is 
often  found  attached  to  the  stems  of  water  weeds.  The 
two  cells  of  unequal  height  are  surrounded  by  a  thin 
transparent  lorica.  For  beauty  of  form  and  delicacy  or 
organization  it  would  be  hard  to  find  anything  surpas- 
sing this  little  creature. 

Vorticella  and  its  allies  are  among  the  commonest 
and  most  ubiquitous  of  protozoans.  They  are  sessile 
and  stalked,  with  some  portion  or  all  of  the  base  con- 
tractile. Vorticella  forms  clusters  of  many  separate 
individuals,  while  Epistylis  forms  branching,  tree-like 
compound  colonies  (fig.  72).  Oftentimes  they  com- 
pletely clothe  twigs  and  grass  stems 
lying  in  the  water,  as  with  a  white 
fringe.  Often  they  cluster  about  the 
appendages  of  crustaceans  and  insects, 
or  thickly  clothe  their  shells.  Some- 
times they  cling  to  floating  algal  fila- 
ments in  the  water-bloom  (see  fig.  179 
on  p.  295). 

Ophrydium  forms  colonies  of  a  very 
different  sort.  Numerous  weak-stalked 
individuals  have  their  bases  imbedded 
in  a  roundish  mass  of  gelatin.  The 
colonies  lie  scattered  about  over  the 
bottom  of  a  lake  or  pond.  They  are  Ths^dedaGrJct^jes^lk?I]; 
roundish,  or  often  rather  shapeless 
masses  varying  in  size  from  mere  specks 
up  to  the  dimensions  of  a  hen's  egg.  In  the  summer  of 
1906  the  marl-strewn  shoals  of  Walnut  Lake  in  Michigan 
were  so  thickly  covered  that  a  boat-load  of  the  soft 
greenish-white  colonies  could  easily  have  been  gathered 
from  a  small  area  of  the  bottom. 

Other  forms  of  protozoa  there  are  in  endless  variety. 
We  cannot  even  name  the  common  ones  here :  but  we 
will  mention  two  that  are  very  different  from  the  fore- 


Fig.  72.    A  colony  of 
Epistylis. 


egg,  probably  the  egg  of 
a  rotifier. 


1 62 


Aquatic  Organisms 


g<  >ing  in  form  and  habit.  Podophrya  will  often  be  encoun- 
ters 1  by  searching  the  backs  of  aquatic  insects  or  the 
sides  <  >f  submerge  d  twigs,  or  other  solid  support,  to  which 
it  is  attached.  It  is  sessile,  and  reaches  out  its  suctorial 
pseiidopodia  in  search  of  soft -bodied  organisms  that  are 
its  prey. 

Anthophysa  is  a  curious  sessile  form  that  is  common 
in  polluted  waters.  It  forms  very  minute  spherical 
colonies  that  are  attached  to  the  transparent  tip  of  a 


Fig.    73.     Three   sessile   protozoans. 

A,  Antnophysa;    B,  Podophrya;    C,  Cothurnia. 

rather  thick  browrnish  stalk.  The  stalk  increases  in 
length  and  diameter  with  age,  occasionally  forking  when 
the  colony  divides.  It  soon  becomes  much  more  con- 
spicuous than  the  colonies  it  carries.  It  often  persists 
after  the  animals  are  dead  and  gone.  After  a  vigorous 
gr<  »wth,  the  accumulated  stalks  sometimes  cover  every 
solid  support  as  with  a  soft  flocculent  brownish  fringe. 
Besides  these  and  other  free-living  forms,  there  are 
parasitic  Protozoa  whose  spores  get  into  the  water. 
Some  of  these  are  pathogenic;  many  of  them  have 
changes  of  host ;  all  of  them  are  biologically  interesting; 
but  wre  have  not  space  for  their  consideration  here. 
We  must  content  ourselves  with  the  above  brief 
mention  of  a  fewr  of  the  more  common  and  interesting 
free-living  forms. 


Aquatic  Organisms  163 

METAZOANS 

Hydras  are  the  only  common  fresh-water  representa- 
tives of  the  great  group  of  Ccelenterates,  so  abundant 
in  the  seas;  and  of  hydras  there  are  but  a  few  species. 
Two  of  these,  the  common  green  and  brown  ones, 
H.  virdis  and  H.  fusca,  are  well  enough  known,  being 
among  the  staples  of  every  biological  laboratory. 
Pedagogically  it  is  a  matter  of  great  good  fortune  that 
this  little  creature  lives  on,  a  common  denizen  of  fresh- 
water pools;  for  its  two-layered  sac-like  body  repre- 
sents well  the  simplest  existing  type  of  metazoan 
structure. 

Hydras  are  ordinarily  sessile,  being  attached  by  a 
disc-like  foot  to  some  solid  support  or  to  the  surface 
film,  from  which  they  often  hang  suspended.  But  at 
times  of  abundance  (and  under  conditions  that  are  not 
at  present  well  understood)  they  become  detached  and 
drift  about  in  the  water.  A  hydra  of  a  brick-red  color 
swarms  about  the  outlet  of  Little  Clear  Pond  at  Saranac 
Inn,  N.  Y.,  in  early  summer,  and  drifts  down  the  out- 
flowing stream,  often  in  such  abundance  that  the  water 
is  tinged  with  red.  The  young  trout  in  hatching  ponds 
through  which  this  stream  flows,  neglect  their  regular 
ration  of  ground  liver,  and  feed  exclusively  upon  the 
hydras,  so  long  as  the  abundance  continues.  The 
hydras  play  fast-and-loose  in  the  stream,  attaching 
themselves  when  they  meet  with  some  solid  support, 
and  then  loosening  and  drifting  again. 

Clear,  sunlit  pools  are  the  favorite  haunts  of  hydras, 
and  the  early  summer  appears  to  be  the  time  of  their 
maximum  abundance.  They  attach  themselves  mainly 
to  submerged  stems  and  leaves,  and  to  the  underside  of 
floating  duckmeat.  They  feed  upon  lesser  animals 
which  abound  in  the  plancton,  and,  multiplying  rapidly 
by  a  simple  vegetative  process  of  budding  with  subs**- 


164 


Aquatic  Organisms 


quent  detachment,  they  become  numerous  when 
plancton  abounds.  Kofoid  ('08)  found  a  maximum 
number  of  5335  hydras  per  cubic  meter  of  water  in 
Quiver  Lake  during  a  vernal  plancton  pulse  in  1S97. 

Fresh-water  sponges  grow  abundantly  in  the  margins 
of  lakes  and  pools  and  in  clear,  slow-flowing  streams. 
They  are  always  sessile  upon  some  solid  support.  In 
sunlight  they  are  green,  in  the  shade  they  grow  pale. 
The  species  that  branch  out  in  slender  finger-like  pro- 
cesses are  most  suggestive  of  plants  in  both  form  and 

color,  but  even  the  slen- 
derest sponge  is  more 
massive  than  any  plant 
body;  and  when  one 
looks  closely  at  the 
surface  he  sees  it  rough- 
ened all  over  with  the 
points  of  innumerable 
spicules,  and  sees  open 
osteoles  at  the  tips.  By 
these  signs  sponges  of 
whatever  form  or  color 
are  easily  recognized. 
The  commonest  sponges  are  low  encrusting  species 
that  grow  outspread  over  the  surfaces  of  logs  and 
timbers.  When,  in  early  summer,  one  overturns  a 
floating  log  that  has  been  long  undisturbed  he  may  find 
it  dotted  with  young  sponges,  growing  as  little  yellow. 
circular,  fleshy  discs,  bristling  with  spicules,  and  each 
with  a  large  central  osteole.  Later  they  grow  irregular 
in  outline,  and  thicker  in  mass.  Toward  the  end  of 
their  growing  season  they  develop  statoblasts  or 
gemmules  (winter-buds)  next  to  the  substratum  (see 
fig.  164  on  p.  264),  and  then  they  die  and  disintegrate. 
So  our  fresh-water  sponges  are  creatures  of  summer, 
*   4ils. 


Fig.     74.     Three    simple    metazoans 

isolated  structural  types. 
.1.  a  scruff  back,  Chatonctw;;    B.  Hydra,  bearing  a 
bud;    C,  a  tardigrade.  Macrobiotus. 


Fresh-Water  Sponges 


165 


All  sponges  are  aquatic,  and  most  of  them  are  marine. 
Only  the  fresh-water  forms  produce  statcblasts,  and 
live  as  annuals. 

In  figure  74  we  show  two  other  simple  metazoans 
(unrelated   to   Hydra  and   of   higher  structural   rank 


Fig.  75.  A  semi-columnar  sponge  from  the  Fulton  Chain  of  Lakes  near  Old 
Forge,  N.  Y.  Half  natural  size.  Photo,  kindly  loaned  by  Dr.  E.  P.  Felt 
of  the  N.  Y.  State  Museum. 


than  the  sponges)  that  during  the  history  of  syste- 
matic zoology,  have  been  much  bandied  about  among 
the  groups,  seeking  proper  taxonomic  associates. 
Chcetonotus  often  appears  on  the  side  of  an  aquarium  jar 
gliding  slowly  over  the  surface  of  the  glass  as  a  minute 
oblong  white  speck.  It  is  an  inhabitant  of  water  con- 
taining plant  infusions,  and  an  associate  of  Paramecium 
which  to  the  naked  eve  it  somewhat  resemble*- 


1 66 


Aquatic  Organisms 


Macrdbiotus  may  be  met  in  the  same  way  and  place, 
but  less  commonlv.  It  may  also  be  taken  in  plancton; 
but  its  favorite  habitat  appears  to  be  tangles  of  water- 
plants,  over  whose  stems  it  crawls  clumsily  with  the  aid 

of  its  four  pairs  of  stub- 
by strong-clawed  feet. 
It  also  inhabits  the 
most  temporary  pools, 
even  rainspouts  and 
stove  urns,  and  is  able 
to  withstand  dessi- 
cation. 

Chaetonotus  is  probably 
most  nearly  related  to 
the  Rotifers;  Macro- 
biotus,  to  the  mites. 

Bryozoans  —  The 
Bryozoans  or  "moss 
animals"  (called  also 
Polyzoans)  are  colonial 
forms  that  are  very 
common  in  fresh  water. 
They  grow  always  in 
sessile  colonies,  which 
have  a  more  or  less 
plant-like  mode  of 
branching .  Their  fixity 
in  place,  their  spreading 
branches  and  the 
brownish  color  of  the 
test  they  secrete  give 
the  commoner  forms 
an  aspect  enough  like  minute  brown  creeping  water 
mosses  to  have  suggested  the  name.  The  individ- 
ual animals  fzooids)  of  a  colony  are  minute,  requir- 
ing a  pocket  lens  for  their  examination,  but  the  colo- 


Fig.  76.  Bryozoan  colonies,  slightly  en- 
larged; a  dense  colony  of  Plumatella  on 
a  grass-stem;  a  beginning  colony  on  a 
leaf  (above) ;  and  a  loosely  grown  colony 
of  Fredericella. 


Bryozoans 


i67 


nies  are  often  large  and  conspicuous.  Two  of  the 
commoner  genera  are  shown  in  figure  76,  natural 
size.  These  may  be  found  in  every  brook  or  pond, 
growing  in  flat  spreading  colonies  on  leaves  or  pieces  of 
bark  or  stones.  Often  a  flat  board  that  has  long  been 
floating  on  the  water,  if  overturned,  will  show  a  com- 
plete and  beautiful  tracery  of  entire  colonies  outspread 
upon  the  surface.  New  zooids  are  produced  by  bud- 
ding. The  buds  remain  permanently  attached,  each 
at  the  tip  of  a  branch.  With  growth  in  length  and  the 
formation  of  a  tough  brown- 
ish cuticle  over  every  por- 
tion except  the  ends,  the 
skeleton  of  the  colony  devel- 
ops. This  skeleton  is  what 
we  see  when  we  lift  the  leaf 
from  the  water  and  look  at 
the  colony — brown,  branch- 
ing tubes,  with  a  hole  in  the 
end  of  each  branch.  Noth- 
ing that  looks  like  an  ani- 
mal is  visible,  for  the  zooids 
which  are  very  sensitive  and 
very  delicate  have  all  with- 
drawn into  shelter.     They 

suddenly  disappear  on  the  slightest  disturbance  of  the 
water,  and  only  slowly  extend  again. 

If  we  put  a  leaf  or  stone  bearing  a  small  colony  into  a 
glass  of  water  and  let  it  stand  quietly  for  a  time  the 
zooids  will  slowly  extend  themselves,  each  unfolding  a 
beautiful  crown  of  tentacles.  There  are  few  more 
beautiful  sights  to  be  witnessed  through  a  lens  than  the 
blossoming  out  of  these  delicate  transparent,  flower- 
like, crowns  of  tentacles  from  the  tips  of  the  apparently 
lifeless  branches  of  a  populous  colony.  They  unfold 
from  each  bud,  like  a  whorl  of  slender  petals  and  slowly 


Fig.  77.     Three  zooids  of  the  bryo- 
zoan,  Plumatella,  magnified. 

I,  expanded ;  m,  retracted;  n,  partly  re- 
tracted; t,  anus;  j,  intestine;  &,  de- 
veloping statoblast. 


1 68 


Aquatic  Organisms 


extend  their  tips  outward  in  graceful  curves.  Then  one 
sees  a  mouth  in  the  midst  of  the  tentacles,  and  water- 
currents  set  up  by  the  lashing  of  the  cilia  which  cover 


Fig.  78.  A  colony  of  Pectinatella,  one-half  natural  size.  Note  the 
distribution  of  buds  in  close  groups  over  the  surface.  The  large 
hole  marks  the  location  of  the  stick  around  which  the  colony  grew. 

them.  A  close  examination  with  the  microscope  will 
reveal  in  each  zooid  the  usual  system  of  animal  organs. 
The  alimentary  canal  is  U-shaped  its  two  openings 
being  near  together  at  the  exposed  end  of  the  body. 


Bryozoans  169 


Several  Bryzoans  secrete  a  gelatinous  covering 
instead  of  a  solid  tube,  and  the  colonies  become  in- 
vested in  a  soft  transparent  matrix.  Pectinatella 
(fig.  78)  is  one  of  these.  It  grows  in  large,  more  or 
less  spherical  colonies,  often  resembling  a  muskmelon 
in  size,  shape  and  superficial  appearance.  It  is  a  not 
uncommon  inhabitant  of  bayous  and  ditches  and  slow- 
flowing  streams.  It  grows  in  most  perfect  spherical 
form  when  attached  to  a  rather  small  twig.  The 
clustered  zooids  form  grayish  rosettes  upon  the  surface 
of  the  huge  translucent  sphere.  Late  in  the  season 
when  statoblasts  appear  the  surface  becomes  thick!  y 
besprinkled  with  brown.  Still  later,  after  the  zooids 
have  died,  and  the  statoblasts  have  been  scattered  the 
supporting  gelatin  persists,  blocks  and  segments  of 
it,  derived  from  disintegrating  colonies,  now  green  from 
an  overgrowth  of  algas,  are  scattered  about  the  shores. 

There  are  but  a  few  genera  of  fresh-water  bryozoans 
■ — some  six  or  seven — and  Plumatella  is  much  the  com- 
monest one.  Plumatella  and  allied  forms  grow  in  water 
pipes.  They  gather  in  enormous  masses  upon  the  sluice- "  \ 
ways  and  weirs  of  water  reservoirs.  They  sometimes 
cover  every  solid  support  with  massive  colonies  of  inter- 
laced and  heaped-up  branches.  Thus  they  form  an 
incrusting  layer  thick  enough  to  be  removed  from  flat 
surfaces  with  shovels.  Its  removal  is  demanded  because 
the  bryozoans  threaten  the  potability  of  the  water  sup- 
ply. They  do  no  harm  while  living  and  active,  but 
when  with  unfavorable  conditions  they  begin  to  die,  N 
their  decomposing  remains  may  befoul  the  water  of  an 
entire  reservoir. 

Cristatella  is  a  flat,  rather  leech-shaped  form  that  is 
often  found  on  the  under  side  of  lily  pads.  ^  It  is  re- 
markable for  the  fact  that  the  entire  colony  is  capable 
of  a  slow  creeping  locomotion.  The  zooids  act  together 
as  one  organism. 


170 


Aquatic  Organisms 


The  free-living  flatworms  abound  in  most  shoal  fresh 
waters.  Some  live  in  shallow  pools;  others  in  lakes 
and  rivers,  others  in  spring-fed  brooks.  They  gather 
on  the  under  sides  of  stones,  sticks  and  trash,  and  con- 
ceal themselves  amid  vegetation,  usually  shunning 
the  light.  They  are  often  collected  unnoticed,  and 
crawl  at  night  from  cover  and  lie  outspread  upon  the 


Fig.  79.     Flatworms. 

A ,  diagram  of  a  planari  in,  showing  food  cavity;  M,  mouth  at  end  of  cylindric  pharynx,  directed 
downward  underneath  the  body;  B,  Dendroccelum;  C,  a  chain  of  five  individuals  of  Stenos- 
tomum  formed  by  automatic  division  of  the  body,  (after  Keller).  Xote  the  anterior  position 
of  the  mouth  and  the  unbranched  condition  of  the  alimentary  canal  in  this  Rhabdocccle  type. 

sides  of  our  aquaria.  We  may  usually  find  the  larger 
species  by  lifting  stones  from  a  stream  bed  or  a  lake 
shore,  and  searching  the  under  side  of  them. 

Flatworms  are  covered  with  vibratile  cilia  and  travel 
from  place  to  place  with  a  slow  gliding  motion.  They 
range  in  length  from  less  than  a  millimeter  to  several 
centimeters.     The  smaller  among  them  are  easily  mis- 


Flatworms  171 


taken  for  large  ciliate  protozoans,  if  viewed  only  with 
the  unaided  eye ;  but  under  the  microscope  the  alimen- 
tary canal  and  other  internal  organs  are  at  once 
apparent.  They  are  multicellular  and  have  little  like- 
ness to  any  infusoria,  save  in  the  ciliated  exterior. 
Most  members  of  the  group  are  flattened,  as  the  com- 
mon name  suggests,  but  a  few  are  cylindric,  or  even 
filiform.  A  few  are  inclined  to  depart  from  shelter  and 
to  swim  in  the  open  water,  especially  at  time  of  abund- 
ance. Kofoid  ('08)  found  them  in  the  channel  waters 
of  the  Illinois  River  in  average  numbers  above  100  per 
cubic  meter,  with  a  maximum  record  of  19250  per  cubic 
meter. 

The  large  flatworms  resemble  leeches  somewhat  in 
form  of  body,  but  they  have  more  of  a  head  outlined 
at  the  anterior  end.  They  lack  the  segmentation  of 
body  and  the  attachment  discs  of  leeches,  and  their 
mode  of  locomotion  is  so  very  different  they  are  readily 
distinguished.  They  do  not  travel  by  loopings  of  the 
body  as  do  leeches,  but  they  glide  along  steadily,  pro- 
pelled by  invisible  cilia. 

The  most  familiar  flatworms  are  the  planarians: 
soft  and  innocuous -looking  little  carnivores,  having 
the  mouth  opening  near  the  midventral  surface  of  the 
body,  and  the  food-cavity  spreading  through  the  body 
in  three  complexly  ramifying  branches.  They  are 
often  brightly  colored,  mottled  white,  or  brick  red,  or 
plumbeous,  and  they  have  a  way  of  changing  color  with 
every  full  meal;  for  the  branched  alimentary  canal 
fills,  and  the  color  of  the  food  glows  through  the  skin 
in  the  more  transparent  species.  The  eggs  of  planarians 
are  often  found  in  abundance  on  stones  in  streams  in 
late  summer.  They  are  inclosed  in  little  brownish 
capsules,  of  the  size  and  appearance  of  mustard  seeds, 
and  each  capsule  is  raised  on  a  short  stalk  from  the 
surface  of  the  stone.     Increase  is  also  by  automatic 


172 


Aquatic  Organisms 


transverse  division  of  the  body,  the  division  plane  lying 
close  behind  the  mouth.  When  a  new  head  has  been 
shaped  on  the  tail-piece,  and  a  new  tail  on  the  head- 
piece, and  two  capable  organisms  have  been  formed, 
then  they  separate.  In  some  of  the  simple  (Rhab- 
doccele)  flatworms  the  body  divides  into  more  than  two 
parts  simultaneously  and  thus  chains  of  new  individuals 
arise  (ng.  79  c). 

Thread-worms  or  Nematodes,  abound  in  all  fresh 
waters,  where  they  inhabit  the  ooze  of  the  bottom,  or 
thick  masses  of  vegetation.  They  are  minute,  color- 
less, unsegmented,  smoothly-contoured  cylindric  worms 
rarely  more  than  a  few  millimeters  long.  The  tail  end 
is  visually  sharply  pointed.  The  mouth  is  terminal  at 
the  front  end  of  the  body,  and  is  surrounded  by  a  few 
short  microscopic  appendages.  Within  the  mouth 
cavity  there  are  often  little  tooth-like  appendages. 
The  alimentary  canal  is  straight  and  cylindric  and 
unappendaged,  and  th^  food  is  semifluid  organic  sub- 
stances. 


/ 

* 

N 

ov 

A 

0 

V                   A           J 

JLady 

hi 

^r— 

^2 

Fig.  80.     Diagram  of  a  Nematode  worm. 

m,  mouth;    n,  nerve  ring;     e,  alimentary  canal;    ov, 
of,  ovaries;  a,  anus.     (After  Jagerskiold). 

We  can  hardly  collect  any  group  of  pond-dwellers 
without  also  collecting  nematodes.  They  may  occupy 
any  crevice.  They  slip  in  between  the  wing-pads  of 
insect  nymphs,  and  into  the  sheaths  of  plant  stems. 
When  we  disturb  the  trash  in  the  bottom  of  our  collect- 
ing dish,  we  see  them  swim  forth,  with  violent  swings 
and  reversals  of  the  pliant  body.  They  may  easily  be 
picked  up  with  a  pipette. 


Bristle-Bearing  Worms 


173 


Oligochetes — Associated  with  the  nematodes  in  the 
trash  and  ooze,  there  is  a  group  of  minute  bristle-bear- 
ing worms,  the  naiads  (Family  Naidse) ,  similar  in  slender- 
ness  and  transparency  of  body,  but  very  different  on 
close  examination;  for  the  body  in  Nais  is  segmented, 
and  each  segment  is  armed  with  tufts  of  bristles  of 
variable  length  and  form.  There  are  many  eomm<  »n 
members  of  this  family.  Besides  the  graceful  Nais 
shown  in  our  figure  there  is  Chcetogaster,  which  creeps 
on  its  dense  bristle-clusters  as  on  feet.  There  is 
Stylaria  with  a  long  tongue-like 
proboscis.  There  is  Dero  that  lives 
at  the  surface  in  a  tube  of  some 
floating  plant  stuffs,  such  as  seeds 
(fig.  82)  or  Lemna  leaves,  slipping 
in  and  out  or  changing  ends  in 
the  tube  with  wonderful  celerity; 
and  there  are  many  others. 

Dero  bears  usually  two  pairs  of 
short  gill-lobes  at  the  posterior  end 
of  the  body. 

All  these  naiads  reproduce  habitually  by  automatic 
division  of  the  body,  which  when  in  process  of  develop- 
ment, forms  chains  of  incompletely  formed  individuals, 
as  in  certain  of  the  natworms  before  described. 

Another  group  of  Oligochetes  is  represented  by 
Tubifex  and  its  allies.  These  dwell  in  the  bottom  mud, 
living  in  stationary  tubes,  which  are  in  part  burrows, 
and  in  part  chimneys  extended  above  the  surface. 
The  worms  remain  anchored  in  these  and  extend  their 
lithe  bodies  forth  into  the  water.  On  disturbance  they 
vanish  instantly,  retreating  into  their  tubes.  They  arc 
often  red  in  color,  and  when  thickly  associated,  as  on. 
sludge  in  the  bed  of  some  polluted  pool,  they  often 
cover  the  bottom  as  with  a  carpet  of  a  pale  mottled 
reddish  color. 


Fig.  81.     Nais.  (after 
Leunis) 


174 


Aquatic  Organisms 


Fig.  82.     Dero,  in  its  case  made  of  floating  seeds. 

Aquatic  earthworms,  more  like  the  well-known 
terrestrial  species,  burrow  deeply  into  the  mud  of  the 
pond   bottom. 

Other  worms  occur  in  the  water  in  great  variety;  we 
have  mentioned  only  a  few  of  the  commonest,  and 
those  most  frequently  seen.  There  are  many  parasitic 
worms  that  appear  in  the  water  for  only  a  brief  period 
of  their  lives:  hair-worms  (Gorditis,  etc.),  which  are 
freed  from  the  bodies  of  insects  and  other  animals  in 
which  they  have  developed;  these  often  appear  in 
watering  troughs  and  were  once  widely  believed  to 
have  generated  from  horse-hairs  fallen  into  the  water. 
There  are  larval  stages  (Cercaria)  of  Cestodes  and 
others,  found  living  in  the  water  for  only  a  brief  interval 

of  passage  from  one 
host  animal  to  an- 
other. There  are 
smaller  groups  also 
like  the  Nemertine 
worms,  sparingly 
represented  in  fresh- 
water ;  for  informa- 
tion concerning 
these  the  reader  is 
referred  to  the 
larger  textbooks  of 
zoology. 


Fig.  83.     Tubifex  in  the  bottom  mud. 


Leeches 


i?5 


Leeches — The  leeches  constitute  a  small  group  whose 
members  are  nearly  all  found  in  fresh-water.  They 
occur  under  stones  and  logs,  in  water- weeds  or  bottom 
mud,  or  attached  to  larger  animals.  The  body  is 
always  depressed,  and  narrowed  toward  the  ends,  more 
abruptly  toward  the  posterior  end  where  a  strong  sucker 
is  developed.  The  front  end  is  more  tapering  and  neck- 
like, and  very  pliant.  There  is  no  distinct  head,  but 
at  the  front  is  a  sort  of  cerebral  nerve  ring  and  there  are 
rudimentary  eyes  in  pairs,  and  surrounding  the  mouth 
is  a  more  or  less  well-developed  anterior  sucker.  The 
great  pliancy  of  the  muscular  body,  the  presence  of  the 
two  terminal  suckers,  and  the  absence  of  legs  or  other 
appendages  determine  the  leech's  mode  of  locomotion. 
It  ordinarily  crawls  about  by  a  series  of  loopings  like  a 
"measuring  worm,"  using  the  suckers  like  legs  for 
attachment.  The  more  elongate  leeches  swim  readily 
with  gentle  undulations  of  the  ribbon-like  body.  The 
shorter  broader  forms  hold  more  constantly  with  the 
rear  sucker  to  some  solid  support,  and  when  detached 
tend  to  curl  up  ventrally  like  an  armadillo. 

Leeches  range  in  size  from  little  pale  species  half  an 
inch  long  when  grown,  to  the  huge  blackish  members 
of  the  horse-leech  group  {Hcemopis)  a  foot  or  more  in 
length.  Many  of  them  are  beautifully  colored  with 
soft  green  and  yellow  tints.  The  much  branched 
alimentary  canal,  when  filled  with  food,  shows  through 
the  skin  of  the  more  transparent  species  in  a  pattern 
that  is  highly  decorative. 

Leeches  eat  mainly  animal  food.  They  are  para- 
sites on  large  animals  or  foragers  on  small  animals  or 
scavengers  on  dead  animals.  Very  commonly  one  finds 
the  parasites  attached  to  the  thinner  portions  of  the 
skins  of  turtles,  frogs,  fishes  and  craw-fishes.  There  is 
no  group  in  which  the  boundary  between  predatory  and 
parasitic  habits  is  less  distinct  than  in  this  one;   many 


i?6 


Anna  tic  Organisms 


leeches  will  make  a  feast  of  vertebrate  blood,  if  occasion 

offers,  or  in  absence  of  this  will  swallow  a  few  worms 

instead. 

The  mouth  of  leeches  is 
adapted  for  sucking,  in  some 
cases  it  is  armed  for  making 
punctures,  as  well:  hence  the 
food  is  either  more  or  less  fluid 
substances  like  blood  or  the 
decomposing  bodies  of  dead 
animals,  or  else  it  consists  of 
the  soft  bodies  of  animals 
small  enough  to  be  swallowe<  1 
whole. 

The  eggs  of  leeches  are 
cared  for  in  various  ways: 
commonly  one  finds  certain 
of  them  in  minute  packets, 
attached  to  stones.  Others 
(Ilccmopis,  etc.)  are  stored  in 
larger  capsules  and  hidden 
amid  submerged  trash.  Oth- 
ers are  sheltered  beneath  the 
body  of  the  parent,  and  the 
young  are  brooded  there  for 
a  time  after  hatching,  as 
shown  in  the  accompanying 
figure.  Nachtrieb  (12)  states 
that  they  are  so  carried  "until 
the  young  are  able  to  move 
about  actively  and  find  a  host 
for  a  meal  of  blood." 
Leeches  are  doubtless  fed  upon  by  many  carnivorous 

animals.  They  are  commonly  reported  to  be  taken 
freely  by  the  trout  in  Adirondack  waters.  In  Bald  Moun- 
tain Pond  they  swim  abundantly  in  the  open  water. 


Fig.  84.  A  clepsine  leech 
(Placobdella  rugosa),  over- 
turned and  showing  the 
brood  of  young  protected 
beneath  the  body.  (From 
the  senior  author's  General 
Biology). 


Rotifers 


17 


// 


The  Rotifers  constitute  a  large  group  of  minute 
animals,  most  characteristic  of  fresh-water.  They 
abound  in  all  sorts  of  situations,  and  present  an  extra- 
ordinary variety  of  forms  and  habits.  Their  habits 
vary  from  ranging  the  open  lake  to  dwelling  symbioti- 
cally  within  the  tissues  of  water  plants ;  from  sojourning 
in  the  cool  waters  of  peren- 
nial springs,  to  running  a 
swift  course  during  the  tem- 
porary existence  of  the  most 
transient  pools.  They  even 
maintain  themselves  in  rain- 
spouts  and  stone  urns,  where 
they  become  desiccated  with 
evaporation  between  times  of 
rain. 

Rotifers  are  mainly  micro- 
scopic, but  a  few  of  the  larger 
forms  are  recognizable  with 
the  unaided  eye.  Often  they 
become  so  abundant  in  pools 
as  to  give  to  the  water  a  tinge 
of  their  own  color.  Grouped 
together  in  colonies  they  be- 
come rather  conspicuous. 
The  spherical  colonies  of  Cono- 

chilus  when  attached  to  leaf -tips,  as  in  the  accom- 
panying picture,  present  a  bright  and  flower-like 
appearance.  Entire  colonies  often  become  detached, 
and  then  they  go  bowling  along  through  the  water, 
in  a  most  interesting  fashion,  the  individuals  jostling 
each  other  as  they  stand  on  a  common  footing,  and 
all  merrily  waving  their  crowns  of  cilia  in  unison.  Often 
a  little  roadside  pool  will  be  found  teeming  with  the 
little  white  rolling  spheres,  that  are  quite  large  enough 
to  be  visible  to  the  unaided  eye. 


Fig.  85.  Three  colonies  of  the 
rotifer,  Conochilus,  attached 
to  the  tips  of  leaves  of  the 
pond-weed,   Nais. 


178 


Aquatic  Organisms 


Melicerta  is  a  large  sessile  rotifer  that  lives  attached 
to  the  stems  of  water-plants  and  when  undisturbed 
protrudes  its  head  from  the  open  end  of  the  tube,  and 
unfolds  an  enormous  four-lobcd  crown  of  waving  cilia. 
It  is  a  beautiful  creature.  Our  picture  shows  the  cases 
of  a  number  of  Melicertas,  aggregated  together  in  a 

cluster,  one  case  serving  as  a 
support  for  the  others. 

The  crown  of  cilia  about  the 

anterior  end  of  the  body  is  the 

most  characteristic  structure 

possessed  by  rotifers.      It    is 

often  circular,  and  the  waving 

cilia  give  it  an  aspect  of  rota- 

fl^  I-  tion,  whence  the  group  name. 

It  is  developed  in   an  extra- 

~J|         |   A  ordinary  variety  of  ways  as 

^&  M  one  may  see  by  consulting  in 

&.  >  any  book  on  rotifers  the  figures 

of  such  as  Stephanoceros,  Flos- 

c  id  an  a,     Synichceta,     Trochos- 

|  ,..  phcera  and  Brachionus. 

k^^B^x  The  cilia  are  used  for  driv- 

Mb^^^,  ing  food  toward  the  mouth 
■L  that  lies  in  their  midst,  and 
for  swimming.  Most  of  the 
forms  are  free-swimming,  and 
many  alternately  creep  and 
swim. 

Brachionus  (fig.  87)  shows 
well  the  parts  commonly  found  in  rotifers.  The  body 
is  inclosed  in  a  lorica  or  shell  that  is  toothed  in  front 
and  angled  behind.  From  its  rear  protrudes  a  long 
wrinkled  muscular  "foot,"  with  two  short  "toes" 
at  its  tip.  Tliis  serves  for  creeping.  The  lobed 
crown  of  cilia  occupies  the  front.      Behind  the  quad- 


FlG.  86.  Two  clusters  of  rotifers 
(Melicerta),  the  upper  but 
little  magnified.  Only  the 
cases  (none  of  the  animals) 
appear  in  the  photographs. 


Rotifers 


]    Q 


rangular  black  eyespot  in  the  center  of  the  body 
appears  the  food  communicating  apparatus  (mastax), 
below  which  lie  ovaries  and  alimentary  canal.  Any 
or  all  the  external  parts  may  be  wanting  in  certain 


Fig.  Sj.     A  rotifer  (Brachionus  entzii)  in  dorsal  and  ven- 
tral views.      (After  France). 

rotifers.  The  smaller  and  simpler  forms  superficially 
resemble  ciliate  infusoria,  but  the  complex  organization 
shown  by  the  microscope  will  at  once  distinguish  them. 
Rotifers  eat  micro-organisms  smaller  than  them- 
selves. They  reproduce  by  means  of  eggs,  often 
parthenogenetically.  The  males  in  all  species  are 
smaller  than  the  females  and  for  some  species  males 
are  not  known. 


i  So 


Aquatic  Organisms 


Molluscs — A  large  part  of  the  population  of  lake  and 
river  beds,  shores,  and  jpools  is  made  up  of  molluscs. 

They  cling,  they 
climb,  they  bur- 
r<  >\v,  they  float — ■ 
they  do  every- 
thing but  swim  in 
the  water.  They 
are  predominantly 
herbivorous,  and 
constitute  a  large 
proportion  of  the 
producing  class 
among  aquatic 
animals.  Two  great 
groups  of  molluscs 
are  common  in 
fresh  water,  the 
familiar  groups  of 
mussels  and  snails. 


F re sh  -water  mus- 
sels (clams,  or 
bivalves)  abound 
in  suitable  places, 
where  they  push 
through  the  mud 
or  sand  with  their 
muscular  protrusi- 
ble  foot,  and  drag 
the  shell  along  in 
a  vertical  position 
leaving  a  channel- 
They  feed  on  micro-organ  - 


FiG.  88.  A  living  mussel,  Anodonta,  with  foot 
retracted  and  shell  tightly  closed.  A  copious 
growth  of  algae  covers  the  portion  of  the 
shell  that  is  exposed  above  the  mud  in  loco- 
motion: the  remainder  is  buried  in  oblique 
position  with  the  foot  projecting  still  more 
deeply  into  the  mud. 


like  trail  across  the  bottom, 
isms. 

The  two  commonest  sorts  of  fresh-water  mussels  are 
roughly  distinguished  by  size  and  reproductive  habits 


Molluscs  1 8 1 


thus :  Unios  and  their  allies  are  large  forms  that  have 
pearly  shells  and  that  live  mainly  in  large  streams  and 
lake  borders.  They  produce  enormous  numbers  of 
young,  and  use  mostly  the  outer  gill  for  a  brood 
chamber.  They  cast  the  young  forth  while  still  minute 
as  glochidia,  to  become  attached  to  and  temporarily 
parasitic  on  fishes.  The  relations  of  these  larval 
glochidia  with  the  fishes  will  be  discussed  in  chapter  V. 
The  lesser  mussels  (family  Sphaeridae)  dwell  in  small 
streams  and  pools  and  in  the  deeper  waters  of  lakes. 
Their  shells  are  not  pearly.  They  produce  but  a  few 
young  at  a  time  and  carry  these  until  of  large  size, 
using  the  inner  gill  for  a  brood-pouch.  The  stouter 
species,  half  an  inch  long  when  grown,  burrow  in  stream- 
beds  like  the  unios.  The  slenderer  species  climb  up 
the  stems  of  plants  by  means  of  their  excessively  mobile 
adhesive  and  flexible  foot.  On  this  foot  the  dainty 
white  mussel  glides  like  a  snail  or  a  flatworm,  up  or 
down,  wherever  it  chooses. 

Snails  are  as  a  rule  more  in  evidence  than  are  mussels, 
for  they  come  out  more  in  the  open.  They  clamber 
on  plants  and  over  every  sort  of  solid  support.  They 
hang  suspended  from  the  surface  film,  or  descend  there- 
from on  strings  of  secreted  mucus.  They  traverse 
the  bottom  ooze.  We  overturn  a  floating  board  and 
find  dozens  of  them  clinging  to  it,  and  often  wre  find 
a  filmy  green  mass  of  floating  algae  thickly  dotted  with 
their  black  shells. 

They  eat  mainly  the  soft  tissues  of  plants,  and  micro- 
organisms in  the  ooze  covering  plant  stems.  A  ribbon- 
like rasp  (radnla)  within  the  mouth  drawn  back  and 
forth  across  the  plant  tissue  scrapes  it  and  comminutes 
it  for  swallowing.  Because  snails  wander  constantly 
and  feed  superficially  without,  as  a  rule,  greatly  altering 
the  form  and  appearance  of  the  larger  plants  on  which 


I  82 


Aquatic  Organisms 


they  feed,  their  work  is  little  noticed;  yet  they  con- 
sume vast  quantities  of  green  tissue  and  dead  stems. 
The  commoner  pond  snails  lay  their  eggs  in  oblong 
gelatinous  clumps  that  are  outspread  upon  the  surfaces 
of  leaves  and  other  solid  supports.  Other  snails  are 
viviparous. 

The  two  principal  groups  of  fresh-water  snails  may 
roughly  be  distinguished  as  (i)  operculate  snails  which 
live  mainly  upon  the  bottom  in  larger  bodies  of  water, 
and  have  an  operculum  closing  the  aperture  of  their 
shell  when  they  retreat  inside,  and  which  breathe  by 


Fig.  89.  Two  pond  snails  (Limited  palustris)  foraging 
on  a  dead  stem  that  is  covered  with  a  fine  growth  of 
the  alga,  Chcetophora  incrassata. 


means  of  gills:  (2)  pulmonate  snails,  which  most 
abound  in  vegetation-filled  shoals,  breathe  by  means  of 
a  simple  lung  (and  come  to  the  surface  betimes,  to  refill 
it  with  air)  and  have  no  operculum. 

The  snails  wre  oftenest  see  are  members  of  three 
genera  of  the  latter  group:  Limncza,  shown  in  the 
accompanying  figure,  having  a  shell  with  a  right-hand 
spiral  and  a  slender  point;  Physa,  having  a  shorter 
spiral,  twisted  in  the  opposite  way,  and  Planorbis, 
shown  in  fig.  65  on  p.  155,  having  a  shell  coiled  in  a  flat 
spiral.  A  ncylus  is  a  related  minute  limpet-shaped  snail, 
having  a  widely  open  shell  that  is  not  coiled  in  a  spiral. 
Its  flaring  edges  attach  it  closely  to  the  smooth  surfaces 
of  plant  stems  or  of  stones. 


Crustaceans  183 


ARTHROPODS 

We  come  now  to  that  great  assemblage  of  animals 
which  bear  a  chitinous  armor  on  the  outside  of  the 
body,  and,  as  the  name  implies,  are  possessed  of  jointed 
feet.  This  group  is  numerically  dominant  in  the  world 
today  on  sea  and  land.  It  is  roughly  divisible  into 
three  main  parts;  crustaceans,  spiders  and  insects. 
The  crustaceans  are  the  most  primitive  and  the  most 
wide-spread  in  the  water-world;  so  with  them  we  will 
begin. 

The  Crustaceans  include  a  host  of  minute  forms,  such 
as  the  water  fleas  and  their  allies,  collectively  known 
as  Entomostraca,  and  a  number  of  groups  of  larger 
forms,  such  as  scuds,  shrimps,  prawns  and  crabs,  col- 
lectively known  as  the  higher  Crustacea  or  Malacos- 
traca.  A  few  of  the  latter  (crabs,  sow-bugs,  etc.)  live 
in  part  on  land,  but  all  the  groups  are  predominately 
aquatic,  and  the  Entomostraca  are  almost  wholly  so. 

The  Entomostraca  are  among  the  most  important 
animals  in  all  fresh  waters.  They  are  perhaps  the  chief 
means  of  turning  the  minute  plant  life  of  the  waters  into 
food  for  the  higher  animals.  They  are  themselves  the 
chief  food  of  nearly  all  young  fishes. 

There  are  three  groups  of  Entomostraca,  so  common 
and  so  important  in  fresh  water,  that  even  in  this  brief 
discussion  we  must  distinguish  them.  They  are: 
Branchiopods,  Ostracods  and  Copepods. 

The  Branchiopods,  or  gill-footed  crustaceans,  have 
some  portion  of  the  thoracic  feet  expanded  and  lamelli- 
form,  and  adapted  to  respiratory  use.  The  feet  are 
moved  with  a  rapid  shuttle-like  vibration  which  draws 
the  water  along  and  renews  the  supply  of  oxygen.  The 
largest  of  the  entomostraca  are  members  of  this  group ; 
they  are  very  diverse  in  form. 


184  Aquatic  Organisms 

The  fairy  shrimp,  shown  in  the  accompanying  figure, 
is  one  of  the  largest  and  showiest  of  Entomostraca.  It 
is  an  inch  and  a  half  long  and  has  all  of  the  tints  of 
the  rainbow  in  its  transparent  body.  It  appears  in 
spring  in  rainwater  pools  and  is  notable  for  its  rapid 
growth  and  sudden  disappearance.  It  runs  its  rapid 
course  while  the  pools  are  filled  with  water,  and  lays 
its  eggs  and  dies  before  the  time  of  their  drying  up. 
The  eggs  settle  to  the  bottom  and  remain  dormant, 
awaiting  the  return  of  favorable  season.  The  animal 
swims  gracefully  on  its  back  with  two  long  rows  of 
broad,  thin,  fringed,  undulating  legs  uppermost,  and 
its  forked  tail  streaming  out  behind,  and  its  rich  colors 

fairly   shimmering    in    the 

^^^^^m^^^^^^  Of  very  different  appear- 

*W&&p*'  x.      ance  js  the  related  mussel- 

FIC'  %SLF$LS&).  C">r°-    shrimp  (Estheria) ,  which  has 

its  body  and  its  long  series 
of  appendages  inclosed  in  a  bivalve  shell.  Swimming 
through  the  water,  it  looks  like  a  minute  clam  a  centi- 
meter long,  traveling  in  some  unaccountable  fashion; 
for  its  legs  are  all  hidden  inside,  and  nothing  but  the 
translucent  brownish  shell  is  visible.  This  shell  is 
singularly  clam-like  in  its  concentric  lines  of  growth  on 
the.  surface  and  its  umbones  at  the  top.  This,  in 
America,  is  mainly  Western  and  Southern  in  its  distri- 
bution, as  is  also  A  pus,  which  has  a  single  dorsal  shell 
or  carapace,  widely  open  below  and  shaped  like  a  horse- 
shoe crab. 

These  large  and  aberrant  Branchiopods  are  all  very 
local  in  distribution  and  of  sporadic  occurrence.  As 
the  seasons  fluctuate,  so  do  they.  But  they  are  so 
unique  in  form  and  appearance  that  when  they  occur 
they  will  hardly  escape  the  notice  of  the  careful  observer 
of  water  life. 


Water- Fleas 


185 


Water-fleas — The  most  common  of  the  Branchiopods 
are  the  water-fleas  (order  Cladocera)  such  as  are  shown 
in  outline  in  figure  91.  These  are  smaller,  more  trans- 
parent forms,  having  the  body,  but  not  the  head,  in- 
closed in  a  bivalve  shell.  The  shell  is  thin,  and  finely 
reticulate  or  striated  or  sculptured,  and  often  armed 
with  conspicuous  spines.  The  post-abdomen  is  thin  and 
flat,  armed  with  stout  claws  at  its  tip  and  fringed  with 
teeth  on  its  rear  margin,  and  it  is  moved  in  and  out 
between  the  valves  of  the  shell  like  a  knife  blade  in  its 
handle.  The  pulsating  heart,  the  circulating  blood,  the 
contracting  muscles,  and  the  vibrating  gill-feet  all  show 
through  the  shell  most 
clearly  under  a  microscope. 
Hence  these  forms  are  very 
interesting  for  laboratory 
study,  requiring  no  prepara- 
tion other  than  mounting 
on  a  slide. 

Some  water-fleas,  like 
Simocephalus,  shown  in  fig- 
ures 91  and  92  swim  freely 
on  their  backs,  in  which 
position  gravity  may  aid 
them  in  getting  food  into  their  mouths.  When  the 
swimming  antennae  are  developed  to  great  size,  as  in 
Daphne  (fig.  91a),  the  strokes  are  slow  and  progress  is 
made  through  the  water  in  a  series  of  jumps.  When 
the  antennae  are  shorter,  as  in  Chydorus  (fig.  91  b),  their 
strokes  are  more  rapidly  repeated,  and  progression 
steadier 

The  Cladocerans  are  abundant  plancton  organisms 
throughout  the  summer  season.  They  forage  at  a  little 
depth  by  day,  and  rise  nearer  to  the  surface  by  night. 

The  food  of  water-fleas  is  mainly  the  lesser  green 
algae  and  diatoms.    They  are  among  the  most  important 


Fig.  91.    Water-fleas 

a,  Daphne;  b,  Chydorus;   c,  Simocephalus; 
d,  Bosmina.     Note  the  "proboscis." 


1 86 


Agnatic  Organisms 


herbivores  of  the  open  water.     They  are  themselves 
important  food  for  fishes. 

The  importance  of  water  fleas  in  the  economy  of 
water  is  largely  due  to  their  very  rapid  rate  of  reproduc- 
tion.    During  the  summer  season  broods  of  eggs  suc- 


Fig.  92.     A  water-flea  (Simocephalus  vetulus)  in  its  ordinary 

swimming  position.  Note  the  striated  shell,  and  the  ali- 
mentary canal,  blackish  where  packed  with  food-residue  in 
the  abdomen. 

cessively  appear  in  the  chamber  enclosed  by  the  shell 
on  the  back  of  the  animal  (see  figure  93)  at  intervals 
of  only  a  few  days.  The  young  develop  rapidly  and 
are  themselves  soon  producing  eggs.  In  Daphne  pulex, 
for  example,  it  has  been  calculated  that  the  possible 


Ostracods  187 


progeny  of  a  single  female  might  reach  the  astounding 
number  of  13,000,000,000  in  sixty  days. 

The  Ostracods  are  minute  crustaceans,  averaging 
perhaps  a  millimeter  in  length,  having  the  head,  body 
and  appendages  all  inclosed  in  a  bivalve  shell.  The  shell 
is  heavier  and  less  transparent  than  that  of  the  water 
fleas.  It  is  often  sculptured,  or  marked  in  broad  patterns 


Fig.  93.     One  of  our  largest  water-fleas,  Eurycerus  lamellatus, 

twenty  times  natural  size.  Note  the  eggs  in  the  brood  chamber 
on  the  back.  Note  also  the  short  beak  and  the  broad  post- 
abdomen  (shaped  somewhat  like  a  butcher's  cleaver)  by  which 
this  water-flea  is  readily  recognized. 

with  darker  and  lighter  colors.  The  inclosed  appenda- 
ges are  few  and  short,  hardly  more  than  their  tips  show- 
ing when  in  active  locomotion.  There  are  never  more 
than  two  pairs  of  thoracic  legs.  The  identification  of 
ostracods  is  difficult,  since,  excepting  in  the  case  of 
strongly  marked  forms,  a  dissection  of  the  animal  fr  >rr 
its  shell  is  first  required, 


iS8 


Aquatic  Organisms 


Fig.  94.  An  Ostracod  {Cypris 
virens),  lateral  and  dorsal  views, 
(after  Sharpe.) 


Some  Ostracods  are  free- 
swimming  (species  of  Cypris, 
etc.)  and  some  (Notodromas ) 
haunt  the  surface  in  sum- 
mer; but  most  are  creeping 
forms  that  live  among 
water  plants  or  that  burrow 
in  the  bottom  ooze.  In  pools  where  such  food  as  algae 
and  decaying  plants  abound  Ostracods  frequently 
swarm,  and  appear  as  a  multitude  of  moving  specks 
when  we  look  down  into  the  still  water. 

Relict  pools  in  a  dry  summer  are  likely  to  be  found 
full  of  them.  Both  sexes  are  constantly  present  in 
most  species  of  Ostracods,  but  a  few  species  are  repre- 
sented by  females  only,  and  reproduce  by  means  of 
unfertilized  eggs. 

The  Cope  pods  are  the  perennial  entomostraca  of  open 
water.  Summer  and  winter  they  are  present.  Three 
of  the  commonest  genera  are  shown  in  figure  95,  toge- 
ther with  a  nauplius — the  larval  form  in  which  the 
members  of  this  group  hatch  from  the  egg.  Nothing  is 
more    familiar    in  laboratory  aquaria  than  the  little 

white  Cyclops  (fig.  96,  swim- 
ming with  a  jerky  motion, 
the  female  carrying  two 
large  sacs  of  eggs. 

A  more  or  less  pear-shaped 

body  tapering  to  a  bifurcate 

tail  at   the   rear,    a   single 

median  eye  and  a  pair  of 

large  swimming  antennae  at 

Fig.  95.    Common  copepods        the  front,  and  four  pairs  of 

c^^^^',)CTo^l     thoracic  swimming  feet 

,   ^iSZSrS&rSE     beneath,     characterize    the 

dl &  n2E the  form  °f  that  appendage     members  of  this  group. 


Copepods 


is9 


The  species  of  Diapt  omits  are  remarkable  for  having 
usually  very  long  antennae  and  often  a  very  lively  red 
color.  Sometimes  they  tinge  the  water  with  red,  when 
present  in  large  numbers. 

Copepods  feed  upon  animals  plancton  and  algae, 
especially  diatoms.  They  are  themselves  important 
food  for  fishes,  especially  for  young  fishes. 

The  higher  Crustacea, 
(Malacostraca)  are  rep- 
resented in  our  fresh 
waters  by  four  distinct 
groups,  all  of  which 
agree  in  having  the 
body  composed  of 
twenty  segments  that 
are  variously  fused 
together  on  the  dorsal 
side,  each,  except  the 
last,  bearing  (at  least 
during  development)  a 
pair  of  appendages. 
Of  these  segments  five 
belong  to  the  head, 
eight  to  the  thorax  and 
the  remainder  to  the 
abdomen.  My  sis  (fig. 
97)  is  the  sole  represen- 
tative of  the  most  primitive  of  these  groups,  the  order 
Mysidacea.  Its  thoracic  appendages  are  all  biramous 
and  undifferentiated;  and  still  serve  their  primal 
swimming  function.  Mysis  lives  in  the  open  waters  of 
our  larger  lakes,  in  their  cooler  depths.  It  is  a  delicate 
transparent  creature  half  an  inch  long. 

The  Scuds  (order  Amphipoda)  are  flattened  lateiv 
and  the  body  is  arched.     The  thoracic  legs  are  adapte*  1 


Fig.  96.     A  female  Cyclops,  with  eggs. 


190 


q untie  Organisms 


for  climbing,  and  the  abdominal  appendages  for  swim- 
ming and  for  jumping.  The  body  is  smooth  and  pale; 
often  greenish  in  color.  The  scuds  are  quick  and  active. 
They  dart  about  amid  green  water-weeds,  usually 
keeping  well  to  shelter,  and  they  swim  freely  and 
rapidly  when  disturbed.  In  figure  98  are  shown 
three  species  that  are  common  in  the  eastern  United 
States. 

The  scuds  are  herbivores,  and  they  abound  among 
green  water  plants  everywhere.  They  are  of  much 
importance  as  food  for  fishes.  They  are  hardy,  and 
capable    of    maintaining   themselves   under    stress    of 


Fig.  97.     Mysis  stenolepis.     (After  Paulmier). 

competition.  They  carry  their  young  in  a 
pectoral  broodpouch  until  well  developed ;  and 
altho  they  are  not  so  prolific  as  are  many 
other  aquatic  herbivores,  yet  they  have  possibilities 
of  very  considerable  increase,  as  is  shown  by  the  fol- 
lowing figures  for  Gammarus  fasciatus,  taken  from 
Embody 's  studies  of  191 2: 

Reproductive  season  at  Ithaca,  Apr.  18th  to  Nov.  3d, 
includes  199  days. 

Average  number  of  eggs  laid  at  a  time  22.     Egg  lay- 
ing repeated  on  an  average  of  1 1  days. 

Age  of  the  youngest  egg-laying  female  39  days :   num- 
ber  of  her  eggs,  6. 

P<    i.ble  orogeny  of  a  single  pair  24221  annually. 

Asellus  ib  the  commonest  representative  of  the  order 
Isopoda;  broad,  dorsally-flattened  crustaceans  of  some- 


Decapoda 


191 


what  larger  size,  that  live  sprawling  in  the  mud  of  the 
bottom  in  trashy  pools.  Their  long  legs  and  hairy 
bodies  are  thickly  covered  with  silt.  Two  pairs  of 
thoracic  legs  are  adapted  for  grasping  and  five  pairs  for 
walking,  and  the  appendages  of  the  middle  abdominal 
segments  are  modified  to  serve  for  respiration.  Asellus 
feeds  on  water-cress  and  on  other  soft  plants,  living  and 
dead,  are  found  in  the  bottom  ooze.  It  reproduces 
rapidly,  and,  in  spite  of  cannibal  habits  when  young. 


Fig.  98.     Three  common  Amphipods. 

A,  Gammarus  limnaus;    B,  Gammanis  fasciatus;    C,  Eucrangonyx  gracilis. 

(Phoio  bv  G.  E.  Embody). 

often  becomes  exceedingly  abundant.  An  adult  female 
of  Asellus  communis  produces  about  sixty  eggs  at  a 
time  and  carries  them  in  a  broodpouch  underneath  her 
broad  thorax  during  their  incubation.  There  is  a  new 
brood  about  every  five  or  six  weeks  during  the  early 
summer  season. 

Both  this  order  and  the  preceding  have  blind 
representatives  that  live  in  unlighted  cave  watery  anu 
pale  half -colored  species  that  live  in  wells. 

The  crawfishes  are  the  commonest  inland  representa- 
tives of  the  order  Decapoda.     These  have  the  thoracic 


192  Aquatic  Organisms 

segments  consolidated  on  the  dorsal  side  to  form  a  hard 
carapace,  and  have  but  five  pairs  of  walking  legs  (as 
the  group  name  indicates),  the  foremost  of  these  bear- 
ing large  nipper-feet.  This  group  contains  the  largest 
Crustacea,  including  all  the  edible  forms,  such  as  crabs, 
lobsters,  shrimps,  and  prawns,  most  of  which  are  marine. 
Southward  in  the  United  States  there  are  fresh-water 
prawns  (Palcouojietes)  of  some  importance  as  fish  food. 

The  eggs  of  crawfishes  are  carried  during  incubation, 
attached  to  the  swimmerets  of  the  abdomen,  and  the 
young  are  of  the  form  of  the  adult  when  hatched.  They 
cling  for  a  time  after  hatching  to  the  hairs  of  the  swim- 
merets by  means  of  their  little  nipper-feet,  and  are 
carried  about  by  the  mother  crawfish. 

Crawfishes  are  mainly  carnivorous, 
their  food  being  smaller  animals, 
dead  or  alive,  and  decomposing  flesh. 
In  captivity  they  are  readily  fed  on 
scraps  of  meat.  Southward,  an  omni- 
vorous species  is  a  great  depredator 
in  newly  planted  fields  of  corn  and 
cotton.  Hankinson  fo8)  reports 
that  the  crawfishes  "form  a  very  ¥?fj^\£^£^££ 
important  if  not  the  chief  food  of 
black  bass,  rock  bass,  and  perch"  in  Walnut  Lake, 
Michigan. 

Spiders  and  Mites  are  nearly  all  terrestrial.  Of  the 
true  spiders  there  are  but  a  few  that  frequent  the  water. 
Such  an  one  is  shown  in  the  initial  cut  on  page  158. 
This   spider  is   conspicuous   ei^  r*irm*-ncr  on  the 

surface  of  the  water,  or  descv  nding  Dcix.  u,L 
in  a  film  of  air  that  shines  lik  s  silver;  but  neither  this 
nor  any  other  true  spider  is  of  so  great  importance  in 
the  economy  of  the  water  as  are  many  other  animals 
that  are  far  less  conspicuous.  In  habits  these  do  not 
differ  materially  from  their  terrestrial  relatives. 


Spiders  and  Mites 


193 


Of  mites  there  is  one  rather  small  family  (Hydrach- 
nidae)  of  aquatic  habits.  These  water-mites  are  minute, 
mostly  rotund  (sometimes  bizarre)  forms  with  unseg- 
mented  bodies,  and  four  pairs  of  long,  slender,  radiating 
legs.  One  large  species  (about  the  size  of  a  small  pea) 
is  so  abundant  in  pools  and  is  so  brilliant  red  in  color 
that  it  is  encountered  by  every  collector.     Others,  tho 


Fig.  100.     An  overturned  female  crawfish  (Cambams  bartoni),  showing 
the  eggs  attached  to  the  swimmerets  (four  thoracic  legs  broken  off). 

smaller,  are  likewise  brilliant  with  hues  of  orange, 
green,  yellow,  brown  pfid  blue,  often  in  striking  patterns. 
Water-mites,  e  *  whe?  too  small  to  be  distinguished 
easily  by  their  form  frc  n  ostracods  or  other  minute 
Crustacea  are  easily  dis  inguished  by  their  manner  of 
locomotion.  They  swim  steadily,  in  one  position; 
not  in  the  jerky  manner  of  the  entomostraca.  The 
strokes  of  their  eight  hair-fringed  swimming  feet  come 


194 


Aquatic  Organisms 


in  such  rapid  succession  that  the  body  is  moved 
smoothly  forward.  A  few  water-mites  that  dwell  in  the 
open  water  of  lakes  are  transparent,  like  other 
members  of  open-water  plancton. 

Water-mites  are  nearly  all  parasitic:  they  puncture 
the  skin  and  suck  the  blood  of  larger  aquatic  animals. 
Certain  of  them  are  common  on  the  gills  of  mussels: 
others  on  the  intersegmental  membranes  of  insects. 


Fig.  ioi.     Water  mites  of  the  genus  Limnochares 

Nothing  is  more  common  than  to  find  clusters  of  red 
mites  hanging  conspicuously  at  the  sutures  of  back- 
swimmers  and  other  water  insects. 

Many  mites  lay  their  minute  eggs  on  the  surface  of 
the  leaves  of  water  plants.  Their  young  on  hatching 
have  but  three  pairs  of  legs. 


Aquatic  Insects  195 

INSECTS 

This  is  the  group  of  animals  that  is  numerically 
dominant  on  the  earth  today.  There  are  more  known 
species  of  insects  than  of  all  other  animal  groups  put 
together.  The  species  that  gather  at  the  water-side 
give  evidence,  too,  of  most  extraordinary  abundance  of 
individuals.  Who  can  estimate  the  number  of  midges 
in  the  swarms  that  hover  like  clouds  over  a  marsh,  or 
the  number  of  mayflies  represented  by  a  windrow  of 
cast  skins  fringing  the  shore  line  of  a  great  lake?  The 
world  is  full  of  them.  Like  other  land  animals  they  are 
especially  abundant  about  the  shore  line,  wThere  condi- 
tions of  water,  warmth,  air  and  light,  favor  organic 
productiveness. 

Nine  orders  of  insects  (as  orders  are  now  generally 
recognized)  are  found  commonly  in  the  water.  These 
are  the  Plecoptera  or  stoneflies;  the  Ephemerida  or 
mayflies;  the  Odonata  or  dragonflies  and  damselflies; 
the  Hemiptera  or  water  bugs;  the  Neuroptera  or  net- 
winged  insects;  the  Trichoptera  or  caddis-flies;  the 
Lepidoptera  or  moths ;  the  Coleoptera  or  beetles ;  and 
the  Diptera  or  true  flies.  These,  together  with  the 
Thysanura  or  springtails,  which  hop  about  upon  the 
surface  of  the  water  in  pools,  and  the  Hymenoptera, 
of  which  a  few  members  are  minute  egg-parasites  and 
which,  when  adult,  swim  with  their  wings,  represent 
the  entire  range  of  hexapod  structure  and  metamor- 
phosis. Yet  the  six-footed  insects  as  a  class  are  pre- 
dominantly terrestrial  It  is  only  a  few  of  the  smaller 
orders,  such  as  t  :  ^eflies  and  tl  ,  *  ay  flies,  that 
are  wholly  aquat;  Jf  the  very  large oro  ts  of  moths, 
beetles  and  true  flies  only  a  few  are  aquati 

Aquatic  insect;  are  mainly  so  in  ther  u  0  ature 
stages ;  the  adul  s  are  terrestrial  or  aerial.  Only  a  few 
adult  bugs  and  beetles  are  commonly  found  in  the 


196 


A  qua  tic  Organisms 


water.     Other  insects  are  there  as  nymphs  or  larvae; 
and,  owing  to  the  great  change  of  form  that  is  undergone 


N 

_ 

• 

s^SjHMSS 

zz 

-/       ^ 

s 

Fig.  102.     The  green  darner  dragonfly,  Anax  Junius;   adult  and  nymph 

skin  from  which  it  has  just  recently  emerged.     Save  for  the  displaced 
wing  rasp<-   he  skin  preserve  £  well  the  form  of  the  immature  st<-  je. 
Photo  '      //.  //.  Knight 

at  the  .1  transformation,  they  ar°.  very  unlike  the 

adults  ppearance.     How  very  '     'fke  the  brilliant 


Aquatic  Insects 


197 


adult  dragonfly,  that  dashes  about  in  the  air  on  shim- 
mering wings,  is  the  sluggish  silt-covered  nymph,  that 
sprawls  in  the  mud  on  the  pond  bottom!  How  unlike 
the  fluttering  fragile  caddis-fly  is  the 
caddis-worm  in  its  lumbering  case ! 

As  with  terrestrial  insects,  so  with 
those  that  are  aquatic,  there  are 
many  degrees  of  difference  between 
young  and  adult,  and  there  are  two 
main  types  of  metamorphosis,  long 
familiarly  known  as  complete  and 
incomplete.  With  complete  meta- 
morphosis a  quiescent  pupal  stage  is 
entered  upon  at  the  close  of  the 
active  larval  life,  and  the  form  of 
the  body  is  greatly  altered  during 
transformation.  Adults  and  young 
are  very  unlike.  Caddis- worms,  for 
example,  the  larvae  of  caddis -flies,  are 
so  unlike  caddis-flies  in  every  exter- 
nal feature,  that  no  one  who  has  not 
studied  them  would  think  of  their 
identity. 

The  caddis-fly  shown  in  the  accom- 
panying figure  is  one  that  is  very 
common  about  marshes,  where  its 
larva  dwells  in  temporary  ponds  and 
pools.  Often  in  early  summer,  the 
bottom  will  be  found  thickly  strewn 
with  larvae  in  their  lumbering  cases. 
Then  they  suddenly  disappear. 
The}  drag  th^ir  cases  into  the  shelter 
of  sedge  chxr  ips  borderii  er  the  ^ools, 
and  tiansform  to  pupae  inside  them.  A  fc  nigh'  later 
they  transform  ,to   adult   caddis-flies,  an  lear  a*: 

shown  in  figure  IC3,  pretty  soft  brown  insects  marked 
wit]  straw-yeliow  in  a  neat  pattern.  The  larva  is 
of  the  form  shown  in  figure  104,  a  stocky  worm-like 


Fig.  103.      Caddis-fly. 
{Limnophilus  sp.) 


198 


Aquatic  Organisms 


Fig.  104.     Caddis-worms:   larva? of  Hales  us  guttifer. 

creature,  half  soft  and  pale 
where  constantly  protected  by 
the  walls  of  the  case  in  which 
it  lives,  and  half  dark  colored 
and  strongly  chitinized  where 
exposed  at  the  ends.  There 
are  stout  claws  at  the  rear 
for  clutching  the  wall  of  the 
case;  there  are  soft  pale  fila- 
mentous gills  arranged  along 
the  side  of  the  abdomen,  and 
there  are  three  spacing  tuber- 
cles upon  th^  r~st  segment 
of  the  abdor  uring 

that  a  fresr.  vater 

shall  be  du  ^ase 

co  flow  ovc  The 

legs  are  direo        ..»rward,  for 


F*g.  105.  The  larval  case  of 
T  ;mnophilus,  attached  end- 
.  ..  to  a  submerged  flag  leaf, 
in  posi "  f  transformation. 


A    Caddis-fly 


199 


f. 

J§* 

Fig.  106.     End  view  of  pupal  case  of  Limno- 
philtis  showing  silken  barrier;    enlarged. 


readier  regress  from 
the  case;  they  reach 
forth  from  the  front 
end,  clutching  any 
solid  support. 

The  larva  of  Lim- 
nophilus  lives  in  the 
case  shown  in  figure 
105.  This  is  a  dwel- 
ling composed  of  flat 
plant  fragments 
placed  edgewise  and 
attached  to  the  out- 
side of  a  thin  silken 
tube. 

The  larva,  living 
in  this  tube,  clam- 
bers about  over  the  vegetation,  jerkily  dragging  its 
cumbrous  case  along,  foraging  here  and  there  where 
softened  plant  tissues  offer,  and  when  disturbed,  quickly 
retreating  inside.  It  frequently  makes 
additions  to  the  front  of  its  case,  and 
casts  off  fragments  from  the  rear;  so 
it  increases  the  diameter  to  accom- 
modate its  own  growth. 

When  fully  grown  and  ready  for 
transformation  the  larva  partially  closes 
the  ends,  spins  across  them  net-like 
barriers  of  silk  to  keep  out  intruders 
while  admitting  a  fresh  water  supply. 
Then  it  molts  its  last  larval  skin 
and  transforms  into  a  pupa  of  r 
form  shown  in  the  accompany1'  njgf  iq 
having  large  compound  eyes,  long  ant  *- 
nae,    broad     externa'    wing-cases    and    Fig.  107.   Pupa  of 


copious  external  g  Is. 


Limnophilus. 


200 


Aquatic  Organisms 


Then  ensues  a  quiescent  period  of  a  fortnight  or  more 
during  which  great  changes  of  form,  both  external  and 
internal,  take  place.  The  stuffs  that  the  larva  accumu- 
lated and  built  into  its  body  during  its  days  of  foraging, 
and  that  now  lie  inert  in  the  soft  white  body  of  the  pupa 
are  being  rapidly  made  over  into  the  form  in  which 
they  will  shortly  appear  in  the  body  of  the  dainty  aerial 
caddis-fly.  However,  the  pupa  is  not  wholly  inactive. 
By  gentle  undulations  of  its  body  it  keeps  the  water 
flowing  about  its  gills;  and  when,  at  the  approach  of 
final  transformation,  its  new  muscles 
have  grown  strong  enough,  it  is  seized 
with  a  sudden  fit  of  activity.  It 
breaks  through  the  barred  door  of 
the  case,  pushes  out,  swims  away, 
and  then  walks  on  the  surface  of  the 
water,  seeking  some  emergent  plant 
stem,  up  which  to  climb  to  a  suitable 
place  for  its  final  transformation. 
There  the  caddis-fly  emerges,  at  first 
limp  and  pale,  but  soon  becoming 
daintily  tinted  with  yellow  and  brown, 
full-fled  ged  and  capable  of  meeting  the 
exigencies  of  life  in  a  new  and  wholly 
different  environment. 

It  is  a  marvelous  change  of  form 
and  habits  that  insects  undergo  in 
metamorphosis — especially  in  com- 
plete metamorphosis.  Such  trans- 
formations as  occur  in  other  groups  are  hardly  com- 
parable with  it.  The  change  from  a  tadpole  to  a  frog, 
or  from  a  nauplius  to  an  adult  copepod,  is  slight  by 
comparison;  for  +here  is  o  cessation  of  activity,  and  no 
consir1  arable  pail  of  th-  1  ody  is  even  temporarily  put 
out  cf  use.  But  in  all  the  hi*  ler  insects  an  extra- 
ordinary reversal  of  development  occurs  at  the  close  of 


Fig.  108.  Pupal  skins 
of  Limnophilus,  left 
at  final  molting  at- 
tached to  a  reed 
above  the  surface  of 
the  water. 


Nymph  and  Larva 


201 


active  larval  life.  The  larval  tissues  and  organs  disin- 
tegrate, and  return  to  a  sort  of  embryonic  condition, 
to  be  rebuilt  in  new  form  in  the  adult  insect. 

With  incomplete  metamorphosis  development  is 
more  direct,  there  is  no  pupal  stage,  and  the  form  of  the 
body  is  less  altered  during  transformation.  Metamor- 
phosis is  incomplete  in  the  stoneflies,  the  mayflies,  the 

dragonflies  and  dam- 
selflies  and  in  the 
water  bugs.  The  im- 
mature stage  we  shall 
speak  of  as  a  nymph. 
All  nymphs  agree  in 
having  the  wings  de- 
velop ed  externally 
upon  the  sides  of  the 
thorax.  Metamor- 
phosis is  complete  in 
all  the  other  orders 
above  mentioned. 
Their  immature 
stage  we  shall  call 
a  larva.  All  larvae  agree  in  having  the  wings  devel- 
oped internally:  they  are  invisible  from  the  outside 
until  the  pupal  stage  is  assumed.  It  should  be 
noted  in  passing  that  ' 'complete"  and  "incomplete" 
as  applied  to  metamorphosis  are  purely  relative  terms. 
There  is  in  the  insect  series  a  progressive  divergence 
in  form  between  immature  and  adult  stages,  and  the 
pupal  stage  comes  in  to  bridge  the  widening  gap 
between. 

There  is  less  change  of  form  in  the  water  bugs  than 
in  any  other  group  of  aquatic  i  ^ects.  The  nymph  of 
the  water  boatman  (fig.  109)  differs  chiefly  f re m  the 
adult  in  the  undevel'  ped  condition  of  its  wings  and 
reproductive  organs.  -  v+ 


Fig.    109.     Water  boatmen    (Corixa),  two 
adults  and  a  nymph  of  the  same  species. 


202  Aquatic  Organisms 


The  groups  of  aquatic  insects  that  are  most  com- 
pletely  given   over   to    aquatic   habits   are   the   more 
generalized  orders  that  were  long  included  in  the  single 
Linna?an  order  Neuroptera  (stoneflies,  mayflies,  dragon- 
flies,  caddis-flies,  etc.)*   Our  knowledge  of  the  immature 
stages  of  aquatic  insects  was  begun  by  the  early  micro- 
scopists  to  whom  reference  has  already  been  made  in 
these   pages:     Swammerdam,    Rcesel,    Reaumur,    and 
their   contemporaries,  f      They    delighted    to    observe 
and    describe    the    developmental    stages    of    aquatic 
insects,  and  did  so  with  rare  fidelity.     After  the  days 
of  these  pioneers,  for  a  long  time  little  attention  was 
paid  to  the  immature  stages,  and  descriptions  of  these 
and  accounts  of  their  habits  are  still  widely  scattered!. 

It  is  during  their  immature  stages  that  most  insects, 
both  aquatic  and  terrestrial  ones,  are  of  economic  im- 
portance. It  is  then  they  mainly  feed  and  grow.  It 
is  then  they  are  mainly  fed  upon.  The  adults  of  many 
groups  eat  nothing  at  all:  their  chief  concern  is  with 
mating  and  egg-laying.  Hence  the  study  of  the  im- 
mature stages  is  worthy  of  the  increased  attention 
it  is  receiving  in  our  own  time.  It  will  be  a  very  long 
time  before  the  life  histories  and  habits  of  all  our 
aquatic  insects  are  made  known,  and  there  is  abundant 
opportunity  for  even  the  amateur  and  isolated  student 
of  nature  to  make  additions  to  our  knowledge  by  work 
[n  this  field. 

♦Under  this  name  (we  still  call  them  Neuropteroids)  the  American  forms 
were  first  described  and  catalogued  by  Dr.  H.  A.  Hagen  in  his  classic  "Synopsis 
of  the  Neuroptera  of  North  America."  (Washington,  1861).  Bugs,  beetles, 
moths  and  flies  have  received  corresponding  treatment  in  systematic  synopses 
of  their  respective  orders,  only  the  adult  forms  being  considered. 

fMuch  of  the  best  of  the  work  of  these  pioneers  has  been  gathered  from 
their  ancient  ponderous  and  rather  inaccessible  tomes,  and  translated  by 
Professor  L.  C.  Miall,  and  reprinted  in  convenient  form  in  his  "Natural  History 
of  Aquatic  Insects"  (London,  1895). 

|The  ipletest  available  accounts  of  tht  .ife  histories  and  habits  of  North 
America  aquatic  insects  have  b^en  published  by  the  senior  author  and  his 
collaborators  in  the  Bulletins  47,  C   .  86  am   124  of  the  New  York  State  Museum 


Stone  flics 


203 


The  stonefiies  (order  Plecoptcra)  are  all  aquatic. 
They  live  in  rapid  streams,  and  on  the  wave-washed 
rocky  shores  of  lakes.  They  are  among  the  most 
generalized  of  winged  insects.  The  adults  are  flat- 
bodied    inconspicuous    creatures    of    secretive    habits. 

Little  is  seen  of 
them    by     day, 
and     less    by 
night,  except 
when  some  bril- 
liant light  by  the 
waterside  at- 
tracts  them  to 
flutter  around  it. 
The  colors    are 
obscure,  being 
predominantly 
black,  brown  or 
gray;  but  the 
diurnally-.acliy£- 
foliage  inhabit- 
ing chloroperlas 
are  pale    green. 
They  take  wing 
awkwardly  and 
fly  rather  slowly, 
and   may  often 
be  caught  in  the 
unaided  hand. 
They  are  readily 
picked  up   with 
xhe    fingers    when    at    rest.     The    wings    (sometimes 
aborted)    are    folded    flat  upon  the  back.     They  are 
rather  irregularly  traversed   with  heavy  veins.     The 
tarsi  are  three- jointea'.     This,  together  with   the   flat- 
tened head,   bare   skin,'   anc    long  forwardly-dr^cted 


Fig.  1 10.     An  adult  stonefly ,  Perln  immarginata. 


204 


Aquatic  Organisms 


antennas,  will  be  sufficient  for  recognition  of  members 
of  this  group. 

Stonefly  nymphs  are  elongate  and  flattened,  and  very 
similar  to  the  adults  in  form  of  body.     They  possess 
always  a  pair  of  tails  at  the  end  of  the  body.     Most  of 
them  have  filamentous  gills 
underneath  the  body,  tho  a 
few  that  live  in  well  aerated 
waters    are    lacking    these. 
The  colors  of  the  nymphs 
are  often  livelier  than  those 
of  the  adults,    they    being 
adorned  with  bright  greens 
and  yellows  in  ornate  pat- 
terns. 

The  nymphs  are  mainly 
carnivorous.  They  feed 
upon  mayfly  nymphs  and 
midge  larvae  and  many 
other  small  animals  occur- 
ring in  their  haunts. 

One  finds  these  nymphs 
by  lifting  stones  from  water 
where  it.  nrns  swiftly,  and 
quickly     inverting 


them. 


TKe_nymphs_  cling  closely 
to    the  under    side    of  the 


Fig.  ii 


The  nymph  of  a  stone- 
flv,  Perla  immarginata. 


(Photo  by  Lucy  Wright  Smith.) 


stones,  lying  flat  with  legs 
outspread,  and  holding  on 
by  means  of  stout   paired 

claws  that  are  like  grappling  hooks.  Their  legs  are 
flattened  i  ,nd  laid  down  against  the  stone  in  such  a 
way  that  hey  offer  little  resistance  to  the  passing 
current  ?eflv  nymphs  are  always  found  associated 

with  fl;  £-bodied  Rjiyfly  rv  nphs.of  similar  form,  and 
with  greenish  net- spinning     addis- worms. 


Mavfl, 


ics 


20 


The   mayflies    (order   EbhemrrhhA    o^      11 
They  live  in  all  U  wafe^Sg  ^ptdTSS 
greatest    diversity    of    situations 
I  he  adults  are  fragile  insects,  hav- 
ing long  fore  legs  that  are  habit- 
ually  stretched  far  forward,   and 
two  or  three  long  tails  that   are 
extended  from  the  tip  of  the  bodv 
backward      The  wings  are  corru- 
gated and  fan  like,  but  not  folded 
and  are  held  vertically  in  repose.' 
1  he  hind  wings  are  smalland  incon- 
spicuous.   The  antenna  are  minute 
and  setaceous.     The  head  is  con- 
tracted below  and  the  mouth  parts 
are    rudimentary.      Thus,     many 
characters  serve  to  distinguish  the 
mayflies  from   other   insects   and 
make  their  group  one  of  the  easiest 
to  recognize. 

Mayflies   are   peculiar   also,    in 
their   metamorphosis.       They 
undergo  a  moult  after  the  assump- 
tion of    the   adult    form.      Thev 
transform   tisually  at  the  surface 
ot   the    water,    and,    leaving   the 
cast-off  nymphal  skin  floating  flv 
away  to  the  trees.    Body  and  wings 
are  then  clothed  in  a  thin  pellicle 
oi  dull  grayish  and  usually  pilose 
skm,   which  is  retained  during  a 
short  period  of  quiescence.    Durin°- 
this  period  (which  lasts  but  a  few 


Fig.  112.  An  adult  may- 
fly, SipUonurus  allern'a- 
tus. 

one  or  two   days) 


minutes  in  Can-   an.;  4*     allies, 
b  it  wn.  ninth     arger     .ns  lasts 
tht  -    ar.   known   as   subimagrv:  or 


206 


Aquatic  Organisms 


duns.  Then  this  outer  skin  is  shed,  and  they  come 
forth  with  smooth  and  shining  surfaces  and  brighter 
colors,  as  imagos,  fully  adult,  and  ready  for  their 
mating  flight.  Lacking  mouth  parts  and  feeding  not 
at  all,  they  then  live  but  a  few  hours. 

There  are  few  phenomena 
of  the  insect  world  more  strik- 
ing than  the  mating  flight  of 
mayflies.  The  adult  males  fly 
in  companies,  each  species 
maneuvering  according  to  its 
habit,  and  the  females  come 
out  to  meet  them  in  the  air. 
Certain  large  species  that  are 
concerted  in  their  season  of 
appearance  gather  in  vast 
swarms  about  the  shores  of  all 
our  larger  bodies  of  freshwater 
at  their  appointed  time.  By 
day  we  see  them  sitting 
motionless  on  every  solid  sup- 
port, often  bending  the  stream- 
side  willows  with  their  weight ; 
and  when  twilight  falls  we  see 
all  that  have  passed  their  final 
molt  swarming  in  untold  num- 
bers over  the  surface  of  the 
water  along  shore. 

The  nymphs  of  mayflies  are  all  recognizable  by  the 
gills  upon  the  back  of  the  abdomen.  These  are 
arranged  in  pairs  at  the  sides  of  some  or  all  of  the  first 
seven  segments.  The  body  terminates  occasionally  in 
two  but  usr  illy  in  three  long  tails.  The  mouth  parts 
arejWmsh edjwjth  many  specialties  for  raking  dia toms 
and  for  rasping  /  <-  ved  stems.  Mayfly  nymphs  are 
among  the  most  impo  t  ar      er\  [  vores  in  all  fresh  waters. 


Fig.  113.  The  nymph  of  the 
mayfly,  Siphlon urus  alter natus. 
[Photo  bv  A>ina  Haven  Morgan.') 


Dr a go  uflics 


207 


The  dragonflies  and  damselflies  (order  Odonata)  are 
all  aquatic.  The  adults  are  carnivorous  insects  that  go 
hawking  about  over  the  surfaces  of  ponds  and  meadows, 
capturing  and  eating  a  great  variety  of  lesser  insects. 
The  larger  dragonflies  eat  the  smaller  ones. 


Fig  114.     An  adult  damselfly,  Iscknura  verticalis,  perchinj 
low  galingale,   Cy perns  diandrus. 


on  the  stem  of  a 


The  form  of  body  in  the  dragonflies  is  peculiar  and 
distinctive.  The  head,  which  is  nearly  overspread  by 
the  huge  eyes,  is  loosely  poised  on  the  apex  of  a  narrow 
prothorax.  The  remainder  of  the  thorax  is  enlarged  and 
the  wings  are  shifted  backward  upo^  i\  and  the  legs 
forward,  adapting  them  fc  ■  pe      ine  on  vertical  stems.. 


208  Agnatic  Organisms 

The  abdomen  is  long  and  slender.  On  the  ventral  side 
of  its  second  and  third  segments,  far  removed  from  the 
openings  of  the  sperm  ducts,  there  is  developed  in  the 
male  a  remarkable  copulatory  apparatus,  that  has  no 
counterpart  in  any  other  insects.  The  venation  of  the 
wings,  also,  is  peculiar,  nothing  like  it  being  found  in 
any  other  order. 

The  dragonflies  hold  their  wings  horizontally  in 
repose.  The  damselflies  are  slender  forms  that  hold 
their  wings  vertically  (or,  in  Lestes,  obliquely  outward) 
in  repose.  Fore  and  hind  wings  are  similar  in  form  in 
the  damselflies;    dissimilar,  in  the  dragonflies. 


Fig.  115.     A  nymph  of  the  damsel- 
fly,  Ischnura  verticalis. 


The  nymphs  of  the  entire  order  are  recognizable  by 
the  possession  of  an  enormous  grasping  labium,  hinged 
beneath  the  head.  This  is  armed  with  raptorial  hooks 
and  spines,  and  may  be  extended  forward  to  a  distance 
several  times  the  length  of  the  head.  It  is  thrust  out 
and  withdrawn  with  a  speed  that  the  eye  cannot  follow. 
It  is  a  very  formidable  weapon  for  the  capturing  of 
living  prey.  It  is  altogether  unique  among  the  many 
modifications  of  insect  mouth  parts. 

Damselfly  nymphs  are  distinguished  by  the  posses- 
sion of  three  flat  lanceolate  gill-plates  that  are  carried 
like  tails  at  the  end  of  the  abdomen.  The  edges  of 
these  :es  are  set  vertically,  and  they  are  swung  from 
side  ie  with  a  sculling  motion  to  aid  the  nymphs  in 

sw  ie. 


Dragonfly  Nymphs  209 


Dragonfly  nymphs  have  their  gills  developed  upon 
the  inner  walls  of  a  rectal  respiratory  chamber,  and  not 
visible  externally.  Hence,  the  abdomen  is  much  wider 
than  in  the  damselflies.  Water  drawn  slowly  into  the 
gill  chamber  through  an  anal  orifice,  that  is  guarded  by 
elaborate  strainers,  may  be  suddenly  expelled  by  the 
strong  contraction  of  the  abdominal  muscles.  Thus 
this  breathing  apparatus,  also,  is  used  to  aid  in  locomo- 
tion. The  body  is  driven  forward  by  the  expulsion  of 
the  water  backward. 

Damselny  nymphs  live  for  the  most  part  clambering 
about  among  submerged  plants  in  still  waters;    a  few 


Fig.  1 16.  The  burrowing  nymph  of  a  Gomphine  dragonfly, 
with  an  elongate  terminal  segment  for  reaching  up 
through  the  bottom  mud  to  the  water. 

cling  to  plants  in  the  edges  of  the  current,  and  a  very 
few  cling  to  rocks  in  flowing  water.  Dragonfly  nymphs 
are  more  diversified  in  their  habits.  Many  of  them 
also  clamber  among  plants,  but  more  of  them  sprawl 
in  the  mud  of  the  bottom,  where  they  lie  in  ambush  to 
await  their  prey.  One  considerable  group  (the  Gom- 
phines)  is  finely  adapted  for  burrowing  in  the  silt  and 
sand  of  the  bottom. 

All  are  very  voracious,  eating  living  prey  in  great 
variety.  All  appear  to  prefer  the  largest  game  they 
are  able  to  overpower.  Many  species  are  arrant  canni- 
bals, eating  their  own  kind  even  when  not  sta  d  to  it. 
As  a  group  they  are  among  the  most  import  arni- 

vores  in  shoal  fresh  waters. 


210 


Aquatic  Organisms 


The  true  bugs  (order  ITcmiptera)  are  mainly  terres- 
trial, and  have  undergone  on  land  their  greatest  differ- 
entiation. The  aquatic  ones  are  usually  found  in  still 
waters  and  in  the  shelter  of  submerged  vegetation. 
Tho  comparatively  few  in  species,  they  are  important 
members  of  the  predatory  population  of  ponds  and 


Fig.  117.     A  giant  water  bug  (Benacus  griseus) 
vertical   surface   under   water, 


clinging  to  a 
natural  size. 


pools.  They  are  often  present  in  great  numbers,  if 
not  in  great  variety.  The  giant  water  bugs  (fig.  117) 
are  amonf  the  largest  of  aquatic  insects.  These  are 
widely  1  1  from  their  habit  of  flying  to  arc  lights, 

falling'  h  them,  and  floundering  about  in  the  dust 

of  villa"".  1 


Water  Bugs 


211 


The  eggs  of  the  giant  water-bugs  are  attached  to 
vertical  stems  of  reeds  just  above  the  surface  of  the 
water.  They  are  among  the  largest  of  insect  eggs. 
Those  of  Benacus  (fig.  118)  are  curiously  striped.  The 
eggs  of  a  smaller,  related  water-bug,  Zaitha or Belo stoma , 
are  attached  by  the  female  to  the  broad  back  of  the 


Fig.  i  i 8.     Eggs  of  Benacus,  enlarged;   the  lower- 
most are  in  process  of  hatching. 


male,  and  are  carried  by  him  during  their  incubation. 
The  nymphs  of  this  family,  on  escaping  from  the  egg 
suddenly  unroll  and  expand  their  flat  bodies,  and  attain 
at  once  proportions  that  would  seem  impossible  on 
looking  at  the  egg  (fig.  119). 

Most  finely  adapted  to  life  in  the  water  9  v-ater 

boatmen  (fig.  109  on  p.  201)  and  the  ^  j  aimers, 


212 


Aquatic  Organisms 


which  swim  with  great  agility  and  are  able  to  remain  for 
a  considerable  time  beneath  the  surface  of  the  water. 
The  eggs  of  these  are  attached  beneath  the  water  to  any 

solid  support.  Most 
grotesque  in  form 
are  the  water-scor- 
pions (Nepidae)  ,  that 
breathe  through  a 
long  caudal  respira- 
tory tube.  The 
eggs  of  these  are  in- 
serted into  soft  plant 
tissues,  with  a  pair 
of  long  processes  on 
the  end  of  each  egg 
left  protruding. 

At  the  shore-line 
we  find  the  creep- 
ing    water-bugs 
among  matted  roots 
edge   of  the 
with    shore 
bugs  and  toad  bugs  just  out  on 

Nymphs  and  adults  alike  are  distinguished  from  the 
members  of  all  other  orders  by  the  possession  of  a 
jointed  puncturing  and  sucking  proboscis  beneath  the 
head,  directed  backward  between  the  fore  legs. 

Nymphs  and  adults  are  found  in  the  water  together 
and  are  alike  carnivorous.  Being  similar  in  form  they 
are  readily  recognized  as  the  same  animal  in  different 
developmental  stages. 

The  net-winged  insects  (Neuroptera)  are  mainly 
terrestrial  or  arboreal.  Two  families  only  have  aquatic 
representatives,  the  Sialididee  and  the  Hemerobiidae, 
and  these  are  so  different,  they  are  better  considered 
separately. 


Fig.  IT9.     A  new-hatched  Bcnacus,  and 
a  detached  egg. 


in  the 
water, 
land. 


Dobsons 


13 


I.  Sialididce — These  are  the  dobsons,  the  fish  flies 
and  the  orl  flies.  The  largest  is  Corydalis,  the  common 
dobson  (fig.  120),  whose  larva  is  the  well  known  "hell- 
grammite",  that  is  widely 
used  as  bait  for  bass.  It 
lives  under  stones  in 
rapids.  It  is  a  "crawler" 
of  forbidding  appearance, 
two  or  three  inches  long 
when  grown,  having  a 
stout,  greenish  black  body, 
sprawling,  hairy  legs,  and 
paired  fleshy  lateral  pro- 
cesses at  the  sides  of  the 
abdomen.  There  is  a 
minute  tuft  of  soft  white 
gills  under  the  base  of  each 
lateral  process.  There  is 
a  pair  of  stout  fleshy  pro- 
legs  at  the  end  of  the  ab- 
domen, each  one  armed 
with  a  pair  of  grappling 
hooks.  The  larvae  of  the 
fish-flies  (Chauliodes)  are 
similar  in  form,  but  smaller 
and  lack  the  gill  tufts  under 

the  lateral  filaments.  The  larva  of  the  orl-fly  differs 
conspicuously  in  having  no  prolegs  or  hooks  at  the  end 
of  the  body,  but  instead,  a  long  tapering  slender 
tail.  Fish-fly  larvae  are  most  commonly  found  clinging 
to  submerged  logs  and  timbers.  Orl-fly  larvae  burrow 
in  the  sandy  beds  of  pools  in  streams  and  in  lake  shores. 
All  appear  to  be  carnivorous,  but  little  is  known  of 
the  feeding  habits  of  either  larvae  or  adults.  Tho  large 
and  conspicuous  insects  they  are  rather  secretive  and 
are  rarely  abundant,  and  they  have  b  ;en  little  observed. 


Fig.  120.     An  adult  female  dob- 
son,   Corydalis   cornuta,  natural 


214 


A  qua  lie  Organisms 


\lul/ 


2.  Hemerobiidce — Of  this  large  family  of  lacc-wings 
but  two  small  genera  (in  our  fauna)  of  spongilla  flics, 
CI i mar ia  and  Sisyra,  have  aquatic  larvae.  The  adults 
are  delicate  little  insects  that  are  so  secretive  in  habits 

and  so  infrequently 
seen  that  they  are 
rare  in  collections. 
Their  larvae  are  com- 
monly found  in  the 
cavities  of  fresh  water 
sponges.  They  feed 
upon  the  fluids  in  the 
body  of  the  sponge. 
They  are  distin- 
guished by  the  posses- 
sion of  long  slender 
piercing  mouthparts, 
longer  than  the  head 
and  thorax  together, 
and  by  paired  ab- 
dominal respiratory  filaments,  that  are  angled  at  the 
base  and  bent  underneath  the  abdomen.  These  larvae 
are  minute  in  size  (6  mm.  long  when  grown)  and  are 
quite  unique  among  aquatic  insect  larvae  in  form  of 
mouthparts  and  in  manner  of  life. 

The  caddis-flies  (order  Trichoptera)  are  all  aquatic, 
save  for  a  few  species  that  live  in  mosses.  They  con- 
stitute the  largest  single  group  of  predominantly  aquatic 
insects.     They  abound  in  all  fresh  waters. 

The  adults  are  hairy  moth-like  insects  that  fly  to 
lights  at  night,  and  that  sit  close  by  day,  with  their  long 
antennae  extended  forward  (see  fig.  1 03  on  p.  1 97) .  They 
are  not  showy  insects,  yet  many  of  them  are  very  dainty 
and  delicately  colored.  They  are  short-lived  as  adults, 
and,  like  the  mayflies,  many  species  swarm  at  the  shore 
line  on  summer  evenings  in  innumerable  companies. 


Fig.  121.     Insect  larvae. 

a,  a  diving-beetle  larva  (Coptolomus  interrogatus)- 
after  Helen  Williamson  Lyman);  b,  a  hellgrammite, 
(Corydalis  cornula,  after  Lintner);  c,  an  orl-fly 
larva    (Sialis   infumata,  after  Maude  H.  Anthony). 


Caddis -flies 


21 


The  larvae  of  the  caddis-flies  mostly  live  in  portable 
cases,  which  they  drag  about  with  them  as  they  crawl 
or  climb ;  but  a  few  having  cases 
of  lighter  construction,  swim 
freely  about  in  them.  Such  is 
Tricenodes,  whose  spirally  wound 
case  made  from  bits  of  slender 
stems  is  shown  in  the  accompany- 
ing figure. 

The  cases  are  wonderful  in 
their  diversity  of  form ,  of  materials 
and  of  construction.  They  are 
usually  cylindric  tubes,  open  at 
both  ends,  but  they  may  be 
sharply  quadrangular  or  trian- 
gular in  cross  section,  and  the 
tube  may  be  curved  or  even  coiled 
into  a  close  spiral*. 

Almost  any  solid  materials  that 
may  be  available  in  the  water  in 

pieces  of  suitable  size  may  be  used  in  their  case  build- 
ing:    sticks,    pebbles,   sand-grains  and  shells  are  the 

staple  materials.  Sticks  may  be 
placed  parallel  and  lengthwise, 
either  irregularly,  or  in  a  con- 
tinuous spiral.  They  may  be 
placed  crosswise  with  ends  over- 
Fig.  123.    The  case  of  the  free-  lapping  like  the  elements  of  a 

nodTsming  larvae  °f   Triae"  stick    chimney,    making    thick 

walls  and  rather  cumbrous  ca  ses. 
However  built,  the  case  is  always  lined  with  the  secre- 
tion from  the  silk  glands  of  the  larva.  This  substance 
is  indeed  the  basis  of  all  case  construction.     The  larva 


Fig.  122.  The  larva  of  a 
spongilla  fly,  Sisyra  after 
Maude  H.  Anthony  j. 


*As  in  Helicopsyche,  (see  fig.  221,  on  page  370)  whose  case  of  finely  textured 
sand  grains  was  originally  described  as  a  new  species  of  snail  shell. 


2l6 


Aquatic  Organisms 


builds  by  adding  pieces  one  by  one  at  the  end  of  the 
tube,  bedding  each  one  in  this  secretion,  which  hardens 
on  contact  with  the  water  and  holds  fast.     Small  snails 

and  mussel  shells  are 
sometimes  added  to  the 
exterior  with  striking 
ornamental  effect,  and 
sometimes  these  are 
added  while  the  protes- 
ting molluscs  are  yet 
living  in  them. 

Some  of  the  micro- 
caddis-flies  (family  Hy- 
droptilidae)  fashion 
"parchment"  cases  of 
the  silk  secretion  alone. 
These  are  brownish  in 
color  and  translucent. 
They  are  usually  com- 
pressed in  form  and 
are  carried  about  on 
edge.  Agraylea  decor- 
ates the  parchment 
with  filaments  of  Spiro- 
gyra,  arranged  concentrically  over  the  sides  in  a  single 
external  layer. 

Some  caddis-worms  build  no  portable  cases  at  all,  but 
merely  barricade  themselves  in  the  crevices  between 
stones,  attaching  pebbles  by  means  of  their  silk  secre- 
tion, and  thus  building  themselves  a  walled  chamber 
which  they  line  with  silk.  In  this  they  live,  and  out  of 
the  door  of  the  chamber  they  extend  themselves  half 
their  length  in  foraging.  Other  caddisworms  construct 
fixed  tubes  among  the  stones,  and  at  the  end  of  the  tube 
that  opens  facing  the  current  they  spin  fine-meshed 
funnel-shaped  nets  of  silk.     These  are  open  up  stream, 


Fig.  124.  Cylindric  sand  cases  of 
one  of  the  Leptoceridae,  (en- 
larged; . 


Caddis-worms 


217 


and  into  them  the  current  washes  organisms  suitable 
for  food.  The  caddis-worm  lies  with  ready  jaws  in  wait 
at  the  bottom  of  the  funnel,  and  cheerfully  takes  what 
heaven  bestows,  seizing  any  bit  of  food  that  may  chance 
to  fall  into  its  net.  These  net-spinners  belong  to  the 
family  Hy  dropsy  chidae. 
When  minute  animals 
abound  in  the  current  the 
caddis-worms  appear  to 
eat  them  by  preference: 
at  other  times,  they  eat 
diatoms  and  other  algae 
and  plant  fragments. 
The  order  as  a  whole  tends 
to  be  herbivorous  and 
many  members  of  it  are 
strictly  so;  but  most  of 
them  will  at  least  vary 
their  diet  with  small  may- 
fly and  midge  larvae  and 
entomostracans,  when 
these  are  to  be  had. 

Caddis -worms  are  more  or  less  caterpillar-like,  but 
lack  paired  fleshy  prolegs  beneath  the  body,  save  for  a 
single  strongly-hooked  pair  at  the  posterior  end.  The 
thoracic  legs  are  longer  and  stronger  and  better  devel- 
oped than  in  caterpillars,  and  they  are  closely  applicable 
to  the  sides  of  the  body,  as  befits  slipping  in  and  out 
of  their  cases.  The  front  third  of  the  body  is  strongly 
chitinized  and  often  brightly  pigmented;  the 
remainder,  that  is  constantly  covered  by  the  case,  is 
thin  skinned  and  pale.  Most  caddis-worms  bear  fila- 
mentous gills  along  the  sides  of  the  abdomen,  but  some 
that  dwell  in  streams  are  gill-less  and  others  have  gills 
in  great  compound  clusters  or  tufts. 


Fig.  125.  The  larva  of  Rhyacophila 
fuscula  in  its  barricade  of  stones, 
exposed  by  lifting  off  a  large  top 
stone. 


21 8  Aquatic  Organisms 

Caddis-fly  pupae  are  likewise  aquatic  (and  this  is 
characteristic  of  no  other  order  of  insects),  and  like  the 
larvae,  they  often  bear  filamentous  gills  along  the  sides 
of  the  abdomen.  They  are  equipped  with  huge  mandi- 
bles that  are  supposed  to  be  of  use  in  cutting  a  way  out 
through  the  silk  just  before  transformation.  The 
mandibles  are  shed  at  this  time.  The  adult  caddis-flies 
are  destitute  of  jaws  and  are  not  known  to  feed;  so 
they  are  probably  short-lived. 


^*»K-~W- 

MRS 

<££& 

i 

Fig.  126.     Eggs  of  Triaenodes. 

The  eggs  of  caddis-flies  usually  are  laid  in  clumps  of 
gelatine.  Sometimes  they  are  arranged  in  a  flat  spiral, 
as  in  Triaenodes,  shown  in  the  accompanying  figure: 
sometimes  they  are  suspended  from  twigs  in  a  ring-like 
loop,  as  in  Phryganea.  Oftener  they  form  an  irregular 
clump.  They  are  usually  of  a  bright  greenish  color, 
but  those  of  the  net  spinning  Hydropsyches,  laid  on 
submerged  stones  in  close  patches  with  little  gelatine, 
are  tinged  with  a  brick-red  color. 

The  moths  (order  Lepidoptera)  are  nearly  all  terres- 
trial. Out  of  this  great  order  of  insects  only  a  few 
members  of  one  small  family  (Pyralidae)  have  entered 
the  water  to  live.  These  live  as  larvae  for  the  most  part 
upon  plants  like  water  lilies  and  pond  weeds  that  are 
not  wholly   submerged.     Hydrocampa,   removed  from 


Moths 


219 


its  case  of  two  leaf  fragments,  looks  like  any  related  land 
caterpillar,   with   its   small  brown  head,   its   strongly 


Fig.  127.  Two  larval  cases  of  the  moth 
Hydrocampa,  each  made  of  two  pieces 
of  Marsilea  leaf.  Upper  smaller  case 
unopened,  larva  inside;  lower  case  opened 
to  show  the  larva,  its  cover  below. 

chitinized  prothorax  and  the  series  of  fleshy  prologs 
underneath  the  abdomen.  By  these  same  characters 
anv  other  aquatic  caterpillar  may  be  distinguished  Irom 
the  members  of  other  orders.     Paraponyx  makes  no 


220 


Aqua  tic  0  rga  n  ism  s 


case,  differs  strikingly  in  being  covered  with  an 
abundance  of  forking  filamentous  gills  which  sur- 
round the  body  as  with  a  whitish  fringe.  It  feeds,  often 
in  some  numbers,  on  the  under  side  of  leaves  of  the  white 
water-lily,  or  about  the  sheathing  leaf  bases  of  the 
broad-leaved  pond  weeds  (Potamogeton). 

El  o  phi  I  a  f  i  (li  call's  lives  on  the  exposed  surfaces  of 
stones  in  running  streams,  dwelling  under  a  silt-covered 
canopy  of  thin-spun  silk,  about  the  edges  of  which  it 
forages  for  algae  growing  on  the  stones.     Its  body  is 


Fig.  128.     Larva  of  Elophila 


depressed,  and  its  gills  are  unbranched  and  in  a 
double  row  along  each  side.  It  spins  a  dome-shaped 
cover  having  perforate  margins  under  which  to  pass 
the  pupal  period.  It  emerges,  to  fly  in  companies  of 
dainty  little  moths  by  the  streamside. 

All  these  aquatic  caterpillars  like  their  relatives  on 
land,  are  herbivorous.  They  are  all  small  species; 
they  are  of  wide  distribution  and  are  often  locally 
abundant. 

The  beetles  (order  Coleoptera)  are  mainly  terrestrial, 
there  being  but  half  a  dozen  of  the  eighty-odd  families 
of  our  fauna  that  are  commonly  found  in  the  water. 
Eoth  adults  and  larvae  are  aquatic,  but,  unlike  the  bugs, 
the    beetles    undergo    extensive    metamorphosis,    and 


Beetles 


221 


larvae  and  adults  are  of  very  different  appearance. 
Beetle  larvae  most  resemble  certain  neuropteroids  of  the 
family  Sialididae  in  appearance,  and  there  is  no  single 
character  that  will  distinguish  all  of  them  (see  fig.  121  on 
p.  214).  Only  a  few  beetle  larvae  (Gyrinids,  and  a  few 
Hydrophilids  like  Berosus)  possess  paired  lateral  fila- 
ments on  the  sides  of  the  abdomen  such  as  are  charac- 
teristic of  all  the  Sialididae. 
Aquatic  beetle  larvae  are 
much  like  the  larvae  of  the 
ground  beetles  (Carabidae) 
in  general  appearance,  hav- 
ing well  developed  legs  and 
antennae  and  stout  rapacious 
jaws. 

Best  known  of  water 
beetles  are  doubtless  the 
1  'whirl  -  i  -  gigs"  (Gyrinidae) , 
which  being  social  in  their 
habits  and  given  to  gyrating 
in  conspicuous  companies  on 
the  surface  of  still  waters, 
could  hardly  escape  the 
notice  of  the  most  casual  ob- 
server. Their  larvae,  how- 
ever, are  less  familiar.  They 
are  pale  whitish  or  yellowish  translucent  elongate  crea- 
tures, with  very  long  and  slender  paired  lateral  ab- 
dominal filaments  along  the  sides  of  the  abdomen. 
They  live  amid  the  bottom  trash  where  they  feed  upon 
the  body  fluids  of  blood  worms  and  other  small 
animal  prey.  Living  often  in  broad  expanses  of  shoal 
water  where  there  are  no  banks  upon  which  to  crawl 
out  for  pupation,  they  construct  a  blackish  cocoon 
on  the  side  of  some  vertical  stem  just  above  the  surface 
of  the  water  and  undergo  transformation  there.     The 


Fig.     I2Q.     A     diving     beetle, 
Dytiscus,  slightly  enlarged. 


222 


Aquatic  Organisms 


eggs  are  often  laid  on  the  under  side  of  floating  leaves 
of  pondwccds. 

The   diving   beetles    (Dytiscidae  and 

■ 1   Hydrophilidae)  are  by  far  the  most  num- 

erous   and   important    of   the    aquatic 

beetles.     These  swarm  in  every  pond 

and   pool,    and    are  among    the   most 

I  important  carnivores  of  all  such  waters. 

They  range  in  size  from  the  big  brown 

i   Dytiscus  (fig.  129)  down  to  little  fellows 

I  a    millimeter  long.     Their    prevailing 

colors  are  brown  or  black,  but  many  of 

Fig.  130.     One  of    the  lesser  forms  are  prettily  flecked  and 

the  lesser  diving 
beetles,  Hydro- 
porus,  seven 
times  natural 
size. 

streaked  with 
yellow  (fig.  130). 
The  eggs  of  the 
Dytiscus  and  of 
other  members 
of  its  family  are 
inserted  singly 
into  punctures  in 
the  tissues  of 
living  plants  (fig. 
131).  Those  of 
the  Hydrophilids 
are  for  the  most 
part  inclosed  in 
whitish  silken 
cocoons  attached 

*-.0  plants  near  the  Pig.    131.     Eggs    of    the    diving    beetle, 

.,,^o^«      r^f      fh^  Dytiscus,  in  submerged  leafstalks,  nearly 

aliricice      01      Lite  readv  for  hatching:     the   larva    shows 

Water.  through  the  shell.     (From  Matheson) 


Beetles 


The  Haliplids  are  a  small  family  of  minute  bee- 
having  larvae  of  unique  form  and  habits.     These  larvae 


Fig  132.  Larvae  of  the  beetle,  Peltodytes, 
in  mixed  algal  filaments,  twice  natural 
size;  below,  a  single  larva  more  highly 
magnified.     (From  Matheson). 

live  among  the  tangled  filaments  of  the  coarser  green 
algas,  especially  Spirogyra,  and  they  feed  upon  the 
contents  of  the  cells  that  compose  the  filaments,  suckir 


224  Aquatic  Organisms 


the  contents  of  the  cells,  one  by  one.  They  are  very 
inert-looking,  stick-like,  creatures  and  easily  pass 
unobserved.  Of  our  two  common  genera  one  (Pelto- 
dytes)  is  shown  in  figure  132.  The  body  is  covered 
over  with  very;  long  stiff  jointed  bristle-like  processes, 
giving  it  a  burr-like  appearance.  The  larva  of  the 
other  genus  (Haliplus)  is  more  stick-like,  has  merely 
sharp  tubercles  upon  the  back,  and  has  the  body  ter- 
minating in  a  long  slender  tail. 

The  Riffle  beetles  (Parnidae  and  Amphizoidce)  prefer 
flowing  water.  They  do  not  swim,  but  clamber  ovei 
the  surfaces  of  logs  and  stones.  They  are  mostly  small 
beetles  of  sprawling  form,  having  stout  legs  that 
terminate  in  curved  grappling  claws.  There  is  great 
variety  of  form  among  their  larvae,  the  better  adapted 
ones  that  live  in  swift  waters  showing  a  marked  ten- 
dency to  assume  a  limpet-like  contour.  This  cul- 
minates in  the  larva  of  Psephenus,  commonly  known  as 
the  "water  penny."  This  larva  was  mistaken  for  a 
limpet  by  its  original  describer.  It  is  very  much 
flattened  and  broadened  and  nearly  circular  in  outline, 
and  the  flaring  lateral  margins  encircling  and  inclosing 
the  body  fit  down  all  round  to  the  surface  of  the  stone 
on  which  it  rests  (see  fig.  160  on  page  260).  Under- 
neath its  body  are  tufts  of  fine  filamentous  gills,  inter- 
segmentally  arranged. 

The  flies  (order  Dipt  era)  are  a  vast  group  of  insects. 

Among  them  are  many  families  whose  larvae  are  wholly 

or  in   part  aquatic.     The  changes  of  form  undergone 

du:  ing  me+    ~L<>rphosis  are  at  a  maximum  in  this  group : 

the  lai    *•  very  different   indeed  from  the  adults. 

j  ip-»  rvae  are  very  diversified  in  form  and 

ilf  ,ure.     The  entire  lack  of  thoracic  legs 

c  .  them  from  all  other  aquatic  larvae. 

little  else  than  this,   and  the  general 


Flies 


225 


tendency  toward  the  reduction  of  the  size  of  the  head 
and  of  the  appendages.  Many  of  them  are  gill-less  and 
many  more  possess  but  a  single  cluster  of  four  tapering 
retractile  anal  gill  filaments. 


Fig.    133.     An  adult  midge,    Tanypus  carneus, 

male. 


By  far  the  most  important  of  the  aquatic  Diptera  in 
the  economy  of  nature  are  the  midges  (Chironomidae). 
These  abound  in  all  fresh  waters.  The  larvae  are 
cylindric  and  elongate,  with  distinct  free  head,  and  body 
mostly  hairless  save  for  caudal  tufts  of  setae.  They  are 
distinguished  from  other  fly  larvae  by  the  possesion  of  a 
double  fleshy  proleg  underneath  the  r-'  >r  x,  1  ad  a 
pair  of  prolegs  at  the  rear  end  of  the  '1  c  paed 

with   numerous   minute   grappling   h'  la 

them  are  of  a  bright  red  color,  and  ne^c'e    jtrfled 

"blood  worms." 


226 


Aquatic  Organisms 


Midge  larvae  live  mainly  in  tubes  which  they  fashion 
out  of  bits  of  sediment  held  together  by  means  of  the 
secretion  of  their  own  silk  glands.  These  tubes  are 
built  up  out  of  the  mud  in  the  pond  bottom  as  shown  in 
the  accompanying  figure,  or  constructed  in  the  crevices 


^  '  ?T 


Fig.  134.     Tubes  of  midge  larvae  in  the  bed  of  a  pool. 


between  leaves,  or  attached  to  stems  or  stones  or  any 
solid  support.  They  are  never  portable  cases.  They 
are  generally  rather  soft  and  flocculent.  The  pupal 
stage  is  usually  passed  within  the  same  tubes  and  the 
pupa  is  equipped  with  respiratory  horns  or  tufts  of 
various  sorts  for  getting  its  air  supply.  The  pupa  (see 
fig.  171  on  p.  279)  is  active  and  its  body  is  constantly 
undulating,  as  in  the  caddisflies. 

The  eggs  of  the  midges  are  laid  in  gelatinous  strings 
ig  plumps  and  are  usually  deposited  at  the  surface  of 
the  water.  Figure  135  shows  the  appearance  of  a  bit 
of  such  an  egg-mass.     This  one  measured  bushels  in 


Fl 


ws 


227 


quantity,  and  doubtless  was  laid  by  thousands  of 
midges.  Figure  136  shows  a  little  bit  of  it— a  portion 
of  a  few  egg  strings— magnified  so  as  to  show  the  form 
and  arrangement  of  the  individual  eggs.  Such  great 
egg  masses  are  not  uncommon,  and  they  foreshadow  the 
coming  of  larvae  in  the  water  in  almost  unbelievable 
abundance. 


Fig.   135.     A  little  bit  of  an  egg  mass  of  the  midge, 
Chironomus,  hung  on  water  weeHs  (Philotria). 

Midge  larvae  are  among  the  greatest  producers  of 
animal  food.  They  are  preyed  upon  extensively,  and 
by  all  sorts  of  aquatic  carnivores. 

Three  families  of  blood-sucking  Diptera  have  aqua  1 '  * 
larvae;  the  mosquitoes  (Culicidas),  the  horseflies 
(Tabanidae)  and  the  black  flies  (Simuliic  e) .     Mosquito 


22S 


Aquatic  Organisms 


larvae  are  the  well  known  "wrigglers"  that  live  in  rain 
water  barrels  and  in  temporary  pools.  They  are 
readily  distinguished  from  other  Dipterous  larvae  by 
their  swollen  thoracic  segments  and  their  tail  fin.  The 
Dupae  are  free  swimming  and  hang  suspended  at  the 
surface  with  a  pair  of  large  respiratory  horns  or  trum- 
pets in  contact  with  the  surface  when  at  rest. 


FlG.  136.     A  few  of  the  component  egg-strings,  magnified. 

The  larvae  of  the  horseflies  are  burrowTers  in  the  mud 
of  the  bottom.  They  are  cylindric  in  form,  tapering 
to  both  ends,  headless,  appendageless,  hairless,  and 
have  the  translucent  and  very  mobile  body  ringed  with 
segmentally  arranged  tubercles.  They  are  carnivorous, 
and  feed  upon  the  body  fluids  of  snails  and  aquatic 
worms  and  other  animals.     The  white  spiny  pupae  are 


Flies  22Q 

formed  in  the  mud  of  the  shore.  The  tiny  black  eggs 
(fig-  138)  are  laid  in  close  patches  on  the  vertical  stems 
or  leaves  of  emergent  aquatic  plants. 

Black  fly  larvae  live  in  rapid  streams,  attached  in 
companies  to  the  surfaces  of  rocks  or  timbers  over 
which  the  swiftest  water  pours.  They  are  blackish, 
and  often  conspicuous  at  a  distance  by  reason  of  their 
numbers.  They  have  cylindric  bodies  that  are  swollen 
toward  the  posterior  end,  which  is  attached  to  the 
supporting  surface  by  a  sucking  disc.  Underneath  the 
mouth  is  a  single  median  proleg,  and  on  the  front  of  the 
head  convenient  to  the  mouth,  there  is  a  pair  of  "fans," 
whose  function  is  to  strain  forage  organisms  out  of  the 
passing  current.  The  full  grown  larva  spins  a  basket- 
like cocoon  on  the  vertical  face  of  the  rock  or  timber, 
and  in  this  passes  its  pupal  stage.  The  eggs  are  laid 
in  irregular  masses  at  the  edge  of  the  current  where  the 
water  runs  swiftest. 

In  like  situations  we  meet  less  frequently  the  net- 
winged  midges  (Blepharoceridae) ,  whose  scalloped  flat 
and  somewhat  limpet-shaped  larvae  are  at  once  recogniz- 
able by  the  possession  of  a  midventral  row  of  suckers 
for  holding  on  to  the  rock  in  the  bed  of  the  rushing 
waters.  The  naked  pupa  is  found  in  the  same  situation 
and  is  attached  by  one  strongly  flattened  side  to  the 
supporting  surface. 

These  five  above-mentioned  families  are  the  ones 
most  given  over  to  aquatic  habits.  Then  there  are 
several  large  families  a  few  of  whose  members  are 
aquatic:  Leptidae,  whose  larvae  live  among  the  rocks 
in  rapid  streams,  hanging  on  and  creeping  by  means  of 
a  series  of  large  paired  and  bifid  prolegs;  Syrphidas, 
whose  larvae  are  known  as  "rat-tailed  maggots"  since 
their  body  ends  in  a  long  flexuous  respiratory  tube, 
which  is  projected  to  the  surface  for  air  when  the  larva 
lives  in  dirty  pools ;   Craneflies  (Tipulidae)  see  fig.  2 1 5  on 


230 


Aquatic  Organisms 


Fig.  137.     The  larva  of  a  horsefly,  Chrysops. 


Fig.  138.  The  eggs 
of  a  horsefly  on 
an  emergent  bur- 
reed  leaf. 


p.  360)  whose  cylindric  tough- 
skinned  larvae  have  their  heads 
retracted  within  the  prothorax, 
and  bear  on  the  end  of  the  abdo- 
men a  respiratory  disc  perforate 
by  two  big  spiracles  and  sur- 
rounded by  fleshy  radiating  fila- 
ments ;  minute  moth -flies — Psycho- 
didae,  (see  fig.  214  on  p.  359) 
whose  slender  larvae  live  amid 
the  trash  in  both  brooks  and 
swales.  Swaleflies  (Sciomyzidae) 
whose  headless  and  appendage- 
less  larvae  hang  suspended  by 
their  posterior  end  from  the  sur- 
face in  still  water;  and  others 
less  common. 

It  is  a  vast  array  of  forms  this 
order  comprises,  this  mighty  group 
of  two-winged  flies,  that  is  still  so 
imperfectly  known;  and  some  of 
the  most  highly  diversified  of  its 
larvae  are  among  the  commoner 
aquatic  ones. 


VERTEBRATES 

There  is  little  need  that  we  should  give  any  extended 
account  of  the  groups  of  back-boned  animals — fishes, 
amphibians,  reptiles,  birds  and  mammals.  In  water  as 
on  land  they  are  the  largest  of  animals,  and  are  all 
familiar.  The  water- dwellers  among  them,  excepting 
the  fishes  and  a  very  few  others,  are  air-breath- 
ing forms  that  are  mainly  descended  from  a  terrestrial 
ancestry.  They  haunt  the  water-side  and  enter  the 
shoals  to  forage  or  to  escape  enemies,  but  they  cannot 
remain  submerged,  for  they  have  need  of  air  to  breathe. 

The  fishes  have  remained  strictly  aquatic.  They 
dominate  the  open  waters  of  the  larger  lakes  and  streams. 
They  have  multiplied  and  differentiated  and  become 
adapted  to  every  sort  of  situation  where  there  is  water 
of  depth  and  permanence  sufficient  for  their  mainten- 
ance. They  outnumber  in  species  every  other  verte- 
brate group. 

Within  the  water  the  worst  enemies  of  fishes  are 
other  fishes;  for  the  group  is  mainly  carnivorous,  and 
big  fishes  are  given  to  eating  little  ones.  Hence,  tho 
all  can  swim,  few  of  them  do  swim  in  the  open  waters, 
and  these  only  when  wTell  grown.  Those  that  so  expose 
themselves  must  be  fleet  enough  to  escape  enemies,  or 
powerful  enough  to  fight  them.  Little  fishes  and  the 
greater  number  of  mature  fishes  keep  more  or  less 
closely  to  the  shelter  of  shores  and  vegetation.  The 
accompanying  diagram,  based  on  Hankinson's  (08) 
studies  at  Walnut  Lake,  Michigan,  represents  the 
distribution  of  fishes  in  a  rather  simple  case.  The 
thirty-one  species  here  present  range  in  adult  size 
from  the  pike  which  attains  a  length  above  three  feet, 
to  the  least  darter  which  reaches  a  length  of  scared y  an 
inch  and  a  half.     One    species    only,    the    whiterish, 

231 


232 


Aquatic  Organisms 


dwells  habitually  in  the  deep  waters  of  the  lake.  One 
other  species,  the  common  sucker,  is  a  regular  inhabit- 
ant of  water  between  fifteen  and  forty  feet  in  depth. 
The  pike,  ranges  the  upper  waters  at  will  pursuing  his 
prey  over  both  depths  and  shoals;  but  he  appears  to 
prefer  to  lie  at  rest  among  the  water-weeds  where  his 


;**■ 


jxtr.  <asmm  ,. 


Fig.  139.  Ale-wives  (Chi pea  pscudoharengus)  on  the  beach  of  Cayuga  Lake, 
after  the  close  of  the  spawning  season.  A  single  large  sucker  lies  in  the 
foreground. 

gr<  it  mottled  back  becomes  invisible  among  the  lights 
and  shadows. 

The  pondweed  zone  on  the  sloping  bottom  between 
five  and  twenty-five  feet  in  depth  is  the  haunt  of  most 
of  the  remaining  species,  including  all  the  minnowrs,  cat- 
fishes,  sunfishes,  and  the  perches.  The  last  named 
wander  betimes  more  freely  into  the  deep  wrater;    all  of 


Distribution  of  Fishe: 


these  forage  in  the  shoals,  especially  at  night.  The 
catfishes  are  more  strictly  bottom  feeders,  and  these 
feed  mainly  at  night.  A  few  species  keep  to  the  close 
shelter  of  thick  vegetation  at  the  water's  edge,  and  one 
species,  the  least  darter,  prefers  to  lie  over  mottled 
marl-strewn  bottoms  at  depth  between  fifteen  and 
twenty  feet. 

So  it  appears  that  some  two-thirds  of  the  species 
have  their  center  of  abundance  in  the  pondweed  zone: 
here,  doubtless  they  best  find  food  and  escape  enemies. 


>^_,- — 'pondweed   zone 

,  whitefish,  i  species. 
c,  pike,  i  species. 
e,  sucker,  i  species. 
n,  perch  and  wall-eye,  2  species. 
o,  bass,     sunfish,    minnow,    e'c. 

10  species. 
r,  catfishes,  2  species. 
s,  mudminnow,  etc.,  3  species. 
x,  least  darter,  1  species. 


Fig.  140.  Diagram  illustrating  the  habit- 
ual distribution  of  the  thirty-one  species 
of  fishes  in  Walnut  Lake,  Michigan. 
Data  from  Hankinson. 


Only  a  few  of  the  stronger  and  swifter  species  venture 
much  into  the  deeper  water:  the  weaklings  and  the 
little  fishes  frequent  the  weed-covered  shoals. 

The  eggs  of  fishes  are  cared  for  in  a  great  variety  of 
ways.  Their  number  is  proportionate  to  the  amount  of 
nurture  they  receive.  No  species  scatters  its  eggs 
throughout  the  whole  of  its  range,  but  each  species 
selects  a  spot  more  or  less  circumscribed  in  which  to  lay 
its  young.  Carp  enter  the  shoals  and  scatter  their  eggs 
promiscuously  over  the  submerged  vegetation  and  the 
bottom  mud  with  much  tumult  and  splashing.  A 
single  female  may  lay  upwards  of  400,000  eggs  a  season. 


234 


[qua tic  Organisms 


Doubtless  many  of  these  eggs  are  smothered  in  mud  and 
many  others  are  eaten  before  hatching.  Suckers  seek 
out  gravelly  shoals,  preferably  in  the  beds  of  streams,  at 
spawning  time.  Dangers  are  fewer  here  and  a  single 
female  may  lay  50,000  eggs.  Yellow  perch  attach  their 
eggs  in  strings  of  gelatin  trailed  over  the  surface  of 
submerged  water  plants.     The  number  per  fish  is  still 


Fig.  141.     A  splash  on  the  surface  made  by  a  carp  in  spc 


further  reduced  to  some  20,000  eggs.  Sunfishes  make 
a  sort  of  nest.  They  excavate  for  it  by  brushing  away 
the  mud  with  a  sweeping  movement  of  the  pectoral  fins. 
Thus  they  uncover  the  roots  of  aquatic  plants  over  a 
circular  area  having  a  diameter  equal  to  the  length  of 
the  fish.  On  these  roots  the  female  lays  her  eggs,  and 
the  male  guards  them  until  they  are  hatched.  With 
this  additional  care  the  number  is  further  reduced  to 
some  5000  eggs.     Sticklebacks  actually  build  a  nest,  by 


Food  of  Fishes  235 


gathering  and  fastening  together  bits  of  vegetation. 
It  is  built  in  the  tops  of  the  weeds — not  on  the  pond 
bottom.  The  nest  is  roughly  spherical,  with  a  hole 
through  the  middle  of  it  from  side  to  side.  Within  the 
dilated  center  of  the  passageway  the  female  lays  her 
eggs:  the  male  stands  guard  over  the  nest.  After  the 
hatching  of  the  eggs  he  still  guards  the  young.  It  is 
said  that  when  the  young  too  early  leave  the  nest,  he 
catches  them  in  his  mouth  and  puts  them  back.  The 
stickleback  lays  only  about  250  eggs. 

Thus  in  their  extraordinary  range  of  fecundity  the 
fishes  illustrate  the  wonderful  balance  in  nature.  For 
every  species  the  number  of  young  is  sufficient  to 
meet  the  losses  to  which  the  species  is  exposed. 

The  food  of  fresh-water  fishes  covers  a  very  wide 
range  of  organic  products ;  but  the  group  as  a  whole  is 
predaceous.  A  few,  like  the  goldfishes  and  golden 
shiners,  are  mainly  herbivorous  and  live  on  algae  and 
other  soft  plant  stuffs.  Others  like  carp  and  gizzard- 
shad  live  mainly  on  the  organic  stuffs  they  get  by 
devouring  the  bottom  ooze.  Many,  either  from  choice 
or  from  necessity,  have  a  mixed  diet  of  plant  and  animal 
foods.  But  the  carnivorous  habit  is  most  widespread 
among  them.  In  inland  waters  they  are  the  greatest 
consumers  of  animal  foods. 

Such  fishes  as  the  pike  which,  when  grown,  lives 
wholly  upon  a  diet  of  other  fishes,  are  equipped  with  an 
abundance  of  sharp  raptorial  teeth.  The  sheepshead 
has  flattened  molar-like  teeth  strong  enough  for  crushing 
shells  and  adapting  it  to  a  diet  of  molluscs.  Other 
fishes,  even  large  ones  like  the  shovel-nosed  sturgeon, 
have  close-set  gill-rakers.  These  retain  ^  for  ; 
the  plancton  organisms  of  the  water  that  is  strained 
through  the  gills.  The  young  of  all  fishes  are  planet <  >n 
feeders. 


230 


Aquatic  Organisms 


The  Am  phi  bia  as  are  the  smallest  of  the  five  great 
groups  of  vertebrates.  They  are  represented  in  our 
fauna  mainly  by  frogs  and  salamanders.  A  few  of  the 
more  primitive  salamanders  (Urodela) ,  such  asNecturus, 
breathe  throughout  life  by  means  of  gills,  and  are 
strictly  aquatic.  A  few  are  terrestrial,  but  most  are 
truly  amphibious.  They  develop  as  aquatic  larvae 
(tadpoles),  having  gills  for  breathing  and  a  fish-like 
circulation:  they  transform  to  air-breathing,  more  or 
less  terrestrial  adult  forms;  and  they  return  to  the 
water  to  lay  their  eggs  in  the  primeval  environment. 


Fig.  142.     A  leopard  fr< 


Rd)ia  pipiens. 


The  period  of  larval  life  varies  from  less  than  two 
months  in  the  toad  to  more  than  two  years  in  the  bull- 
frog. 

The  eggs  of  amphibians  are,  for  the  most  part,  de- 
posited in  shallow  water,  often  in  masses  in  copious 
gelatinous  envelopes  (see  fig.  201  on  p.  342).  In  some 
cases  the  egg  masses  are  large  and  conspicuous  and  well 
known.  Examples  are  the  long  egg-strings  of  the  toad 
that  lie  trailing  across  the  weeds  and  the  bottom;  or 
the  half-floating  masses  of  innumerable  eggs  laid  by  the 
larger  frogs.  The  eggs  of  the  smaller  frogs  are  less 
often  seen,  those  of  the  peeper  being  attached  singly 
to  plant  stems.  Dr.  A.  H.  Wright  (14)  has  shown  that 
the  eggs  of  all  our  species  of  frogs  are  distinguishable 
by  size,  color,  gelatinous  envelopes  and  character  of 
cluster. 


Amphibians 


Adult  amphibians  are  carnivorous.  They  all  eat 
lesser  animals  in  great  variety.  Frogs  and  toads  have 
a  projectile  and  adhesive  tongue  which  is  of  great  service 
in  capturing  flying  insects;  but  they  eat,  also,  many 
other  less  active  morsels  of  flesh  that  they  find  on  the 
ground  or  in  the  water. 
The  food  of  some  of  the 
lesser  stream-inhabiting 
salamanders ,  such  as 
Spelerpes,  is  mainly  in- 
sects, while  that  of  the 
vermilion-spotted  newt 
is  mainly  molluscs. 

The  amphibia  are  a 
group  of  very  great  bio- 
logical interest.  They 
represent  a  relatively 
simple  type  of  vertebrate 
structure.  Their  devel- 
opment can  be  followed 
with  ease  and  it  is  illumi- 
nating and  suggestive  of 
the  early  evolutionary  history  of  the  higher  verte- 
brates. They  illustrate  in  their  own  free-living  forms 
the  transition  from  aquatic  to  terrestrial  life.  And  they 
show  in  the  different  amphibian  types  many  grades  of 
metamorphosis.     The  transformation  is  more  extensive 


Fig.  143.  Diagram  of  individual  eggs 
from  the  egg  mass  of  the  toad  and 
seven  species  of  frog  occurring  at 
Ithaca.  Eggs  solid  black;  gelati- 
nous envelopes  white.  (After 
Wright). 

A,  Toad,  eggs  in  double  gelatinous  tubes,  form- 
ing strings,  the  inner  tube  divided  by  cross 
partitions;  B,  pickerel  frog;  C,  peeper  (no 
outer  envelope) ;  D,  green  frog  (inner  en- 
velope ellipitical) ;  E,  tree  frog  (outer  en- 
velope ragged) ;  F,  bull  frog  (no  inner 
envelope);  G,  leopard  frog;  H,  wood  frog. 
All  twice  natural  size. 


Fig.  144.    The  spotted  salamander,  Ambystoma  tigrinum. 


238 


Aquatic  Organisms 


in  frogs    than    in    any    other    vertebrates,    involving 
profound  changes  in  internal  organs  and  in  manner  of 

life. 

The  reptiles  are  mainly  terrestrial.     Southward  there 
are  alligators  in  the  water,  but  in  our  latitude  there  are 


Fig.  145.     The  common  snapping  turtle. 


only  a  few  turtles  and  water  snakes.  These  make  their 
nests  on  land.  They  hide  their  eggs  in  the  sand  or  in 
the  midst  of  marshland  rubbish,  where  the  sun's 
warmth  incubates  them. 

These  also  are  carnivorous. 


Water  Bird: 


239 


The  water  birds,  tho  more  numerous  than  the  two 
preceding  groups,  are  but  a  handful  of  this  great  class 
of  vertebrates. 

The  principal  kinds  of  birds  that  frequent  the  water 
are  water-fowl— ducks,  geese  and  swans;  the  shore 
birds— plover,  snipe  and  rails;  the  gulls,  the  herons 
and  the  divers.     Some  of  these  that,  like  the  loon,  are 


Fig.  146.     Wild  geese  foraging  in  a  marsh  in  Dakota. 

superably  fitted  for  swimming  and  diving,  feed  mainly 
on  fishes.  Most  water  birds  consume  a  great  variety  of 
lesser  animals.  The  ducks  and  rails  differ  much  in  diet 
according  to  species.  Thus  the  Sora  rail  eats  mainly 
seeds  of  marsh  plants,  while  the  allied  Virginia  rail  in 
the  same  locality  eats  miscellaneous  animal  food  to  the 
extent  of  more  than  fifty  per  cent,  of  its  diet. 

Only  the  waterfowl  that  are  prized  as  game  birds  are 
extensively  herbivorous.  They  eat  impartially  tne 
vegetable  products  of  the  land  and  of  the  water.     The 


240 


Aquatic  Organisms 


wild  ducks  and  geese  eat  great  quantities  of  duckmeat 
(Lemna)  and  succulent  submerged  aquatics.  Canvas- 
backs  fatten  on  the  wild  celery  (Vallisneria).  In 
Cayuga  Lake  in  winter  they  gorge  themselves  with  the 
starch-filled  winter  buds  of  the  pondweed,  Potamogcton 


Fig.     147.     Floating  nest  of  pied-billed  grebe  (Podilymhus  podireps)  in 

a  cat-tail  marsh,  surrounded  by  water. 

pus  ill  us.  They  also  dive  and  pluck  up  from  the  bottom 
mud  the  reproductive  tubers  of  the  pondweed,  Potamoge- 
ton  pectinatus  (see  fig.  228  on  p.  381). 

Water  birds,  having  attained  the  freedom  of  the  air, 
*r;\  wide   anging  beyond  all  other  animals.     They  come 

d  go        annual  migrations.     They  settle  here  and 


Aquatic  Mammals 


241 


there,  and  commit  local  and  intermittent  depredations. 
The  water  birds  nest  mainly  on  land,  and  in  their 
nesting  and  brooding  habits  they  differ  little  from  their 
terrestrial  relatives. 

The  aquatic  mammals  of  inland  waters  fall  mainly  in 
two  groups,  the  carnivores  and  the  rodents.  Here 
again,  the  carnivores  that  are  more  expert  swimmers 
and  divers,  such  as  fisher,  martin,  otter  and  mink  are 
all  fish-eating  animals.     They  have  become  fitted  to 


Fig.  148.     A  muskrat,  Fiber  zihethicus. 

utilize  the  chief  animal  product  of  the  water.  Of  these 
four  the  mink  alone  has  withstood  the  "march  of 
progress,' '  and  retains  its  former  wide  distribution. 

Of  rodents  there  are  two  fur-bearers  of  much  import- 
ance, the  beaver,  now  driven  to  the  far  frontier,  and  the 
muskrat.  The  muskrat  has  become  under  modern 
agricultural  conditions  the  most  important  aquatic  mam- 
mal remaining.  By  reason  of  its  rapid  rate  of  repro- 
duction, its  ability  to  find  a  living  in  any  cat-tail  marsh, 
big  or  little,  and  its  hardiness,  it  has  been  able  to  main- 
tain its  place. 


CHAPTER   V 


ADJUSTMENT  TO   CONDITIONS 
OF   AQUATIC   LIFE 


INDIVIDUAL 

ADJUSTMENT 


O  infinitely  varied  are 
the  fitnesses  of  aqua- 
tic organisms  for  the 
conditions  they  have 
to  meet  that  we  can 
only  select  out  of  a 
worldf  ul  of  examples  a 
few  of  the  more  wide- 
spread and  significant. 
We  shall  have  space 
here  for  discussing 
only  such  adaptations  to  life  in  the  water  as  are  common 
to  "large  groups  of  organisms,  and  represent  general 
modes  of  adjustment.  First  we  will  consider  some  of 
the  ways  in  which  the  species  is  fitted  to  the  aquatic 
conditions  under  which  it  lives,  and  then  we  will  take 
note  of  some  mutual  adjustments  between  different 
species. 

The  first  of  living  things  to  appear  upon  the  earth 
were  doubtless  simple  organisms  that  were  far  from 

242 


Flotation 


243 


being  so  small  as  the  smallest  now  existing,  or  so  large 
as  the  largest.  They  grew  and  multiplied.  They 
differentiated  into  plants  and  animals,  into  large  and 
small,  into  free-swimming  and  sedentary.  Some  be- 
took themselves  to  the  free  life  of  the  open  waters  and 
others  to  more  settled  habitations  on  shores.  The 
open -water  forms  were  nomads,  forever  adrift  in  the 
waves:  the  shoreward  forms  might  find  shelter  and  a 
quiet  resting  place. 

LIFE   IN   OPEN   WATER 

In  the  open  water  there  are  certain  great  advantages 
that  lie  in  minuteness  and  in  buoyancy.  These  quali- 
ties determine  the  ability  of  organisms  to  float  freely 
about  in  the  more  productive  upper  strata  of  water. 
To  descend  into  the  depths  is  to  perish  for  want  of 
light.  So  the  members  of  many  groups  are  adapted  for 
floating  and  drifting  about  near  the  surface.  These 
constitute  the  planet 071. 

On  the  other  hand,  large  size  has  its  advantages  when 
coupled  with  good  ability  for  swimming  and  food 
gathering.  In  the  rough  world's  strife  the  battle  is 
usually  to  the  strong.  It  is  the  larger,  wide-ranging, 
free-swimming  organisms  that  dominate  the  life  of  the 
open  water.     These  constitute  the  necton. 

Plancton  and  necton  wTill  be  discussed  in  the  next 
chapter  as  ecological  groups,  but  in  this  place  we  may 
take  note  of  the  two  very  different  sorts  of  fitness,  that 
they  have  severally  developed  for  life  in  the  open  water. 
the  plancton  organisms  being  fitted  for  flotation,  and 
the  necton  for  swimming. 

Flotation — All  living  substance  is  somewhat  heavier 
than  water  (i.  e.  has  a  specific  gravity  greater  than  1 
and  therefore  tends  to  sink  to  the  bottom.     T'l  e  vel<  >c- 


244      Adjustment  to   Conditions  of  Aquatic  Life 

ity  in  sinking  is  determined  by  several  factors,  one  of 
which  is  external  and  the  others  are  internal: 

The  external  factor  is  the  varying  viscosity  of  the 
water. 

The  internal  factors  are  specific  gravity,  form  and 
size. 

We  have  mentioned  (p.  30)  that  the  viscosity  of  the 
water  is  twice  as  great  at  the  freezing  point  as  at 
ordinary  summer  temperatures;  which  means,  of  course, 
that  the  water  itself  would  offer  much  greater  resistance 
to  the  sinking  of  a  body  immersed  in  it.  We  are  here 
concerned  with  the  internal  factors. 

Lessening  of  specific  gravity — The  bodies  of  organisms 
are  not  composed  of  living  substance  alone,  but  con- 
tain besides,  inclusions  and  metabolic  products  of 
various  sorts,  which  oftentimes  alter  their  specific 
gravity.  The  shells  and  bone  and  other  hard  parts  of 
animals  are  usually  heavier  than  protoplasm;  the  fats 
and  gelatinous  products  and  gases  are  lighter.  We 
know  that  the  fats  of  vertebrates,  if  isolated  and  thrown 
upon  the  water,  will  float;  and  that  a  fat  man,  in  order 
to  maintain  himself  above  the  water,  needs  put  forth 
less  effort  than  a  lean  one.  There  are  probably  many 
products  of  the  living  body  that  are  retained  within 
or  about  it  and  that  lessen  its  specific  gravity,  but  the 
commonest  and  most  important  of  these  seem  to  fall 
into  three  groups: 

1.  Fats  and  oils,  which  are  stored  assimilation 
products.  These  are  very  easily  seen  in  such  plancton 
organisms  as  Cyclops  (see  fig.  96  on  p.  189)  where  they 
show  through  the  transparent  shell  as  shining  yellowish 
oil  droplets.  Most  plancton  algae  store  their  reserve 
food  products  as  oils  rather  than  as  starches. 

2.  Gases,  which  are  by-products  of  assimilation,  and 
are  distributed  in  bubbles  scattered  through  the  tissue 


Flotation  2i; 


where  produced,  or  accumulate  in  special  containers. 
These  greatly  reduce  the  specific  gravity  of  the  body, 
enabling  even  heavy  shelled  forms  (see  p.  159)  to  float. 

3.  Gelatinous  and  mucilaginous  products  of  the  1  >odv 
which  usually  form  external  envelopes  (see  fig.  10  on 
p.  52)  but  which  may  appear  as  watery  swellings  of  the 
tissues.  Their  occurrence  as  envelopes  is  very  common 
with  plants  and  with  the  eggs  of  aquatic  animals;  thev 
may  serve  also  for  protection  and  defense,  and  for 
regulating  osmotic  pressure,  but  by  reason  of  their  low- 
specific  gravity  they  also  serve  for  flotation. 

Improvment  of  form — We  have  already  called  atten- 
tion (p.  42)  to  the  fact  that  size  has  much  to  do  with  the 
rate  of  sinking  in  still  water.  This  is  because  the 
resistance  of  the  water  comes  from  surface  friction  and 
the  smaller  the  body  the  greater  the  ratio  of  its 
surface  to  its  mass.  Given  a  body  small  enough,  its 
mere  minuteness  will  insure  that  it  will  float.  But  in 
bodies  of  larger  size  relative  increase  in  surface  is 
brought  about  in  various  ways: 

1 .  By  extension  of  the  cell  in  slender  prolongations 
(see  fig.  50,  j,  k,  1,  on  p.  129). 

2 .  By  the  aggregation  of  cells  into  expanded  colonies  : 

a.  Discoid  colonies,  as  in  Pediastrum  (fig.  44  on 

P-  123). 

b.  Filaments,  as  in  Oscillatoria  (fig.  34  on  p.  109). 

c.  Flat  ribbons  of  innumerable  slender  cells  placed 
side  by  side,  as  in  many  lake  diatoms  (Fragil- 
laria,  Tabelaria,  Diatoma). 

d.  Radiate  colonies  as  in  Asterionella  (fig.  35  //  on 
p.  in). 

e.  Spherical  colonies  as  in  Volvox  (fig.  31,  p.  105: 
see  also  a  b  c  of  fig.  50  on  p.  129),  wherein  the 
cells  are  peripheral  ana  widely  separated   the 


246      Adjustment  to  Conditions  of  Aquatic  Life 

interstices   and    the   interior    being   filled   with 
gelatinous  substances  of  low  specific  gravity. 
f.     Dendritic  colonies,  as  in  Dinobryon  (fig.  32  on 
p.  106). 

3.     In  the  Metazoa,  by  the  expansion  of  the  external 
armor  and  appendages  into  bristles,  spines  and  fringes. 
Thus  in  the  rotifer  Notholcalongispina(fig.  149), 
a  habitant  of  the  open  water  of  lakes,  there  is  a 
great  prolongation  of  the  angles  of  the  lorica, 
before  and  behind ;  and  in  the  Copepods  (fig.  95, 
p.   188)  there  is  an   extensive  development  of 
bristles  upon  antennae  and  caudal  appendages. 
Expansions  of  the  body,  if  mere  expansions, 
serve  only  to  keep  the  body  passively  afloat ;  but 
many  of  them  have  acquired  mobility,  becom- 
ing locomotor  organs.     Cilia  and  flagella  are  the 
simplest  of  these,  and  are  common  to  plants  and 
animals.     Almost  all   the  appendages    of  the 
higher  animals,  antennas,  legs,  tails,  etc.,  are 
here  and  there  adapted  for  swimming.    A  body 
whose  specific  gravity  is  but  little  greater  than 
that  of  the  water  may  be  sustained  by  a  mini- 
mum use  of  swimming  apparatus.     The  lesser 
A!on|-    flagellate   and   ciliate    forms,  both    plant  and 
spin  cd    animal,  maintain  their  place  by  continuous  lash- 
rotifer.     -ng  Q£  ^e  water.     If  we  watch  a  few  waterfleas 
in  a  breaker  of  clear  water  we  shall  see  that  their  swim- 
ming also,  is  unceasing.    Each  one  swims  a  few  strokes 
of  the  long  antennae   upward,  and  then   settles  with 
bristles  all  outspread,  descending  slowly,  as  resistance 
yields,  to  its  former  level.     This  it  repeats  again  and 
again.     It  may  turn   to  right  or  to  left,  rise  a  little 
higher  or  sink  a  1"ttle  lower    betimes,  but  it  keeps  in 
the  main  to  its,       ™e-  level.       Its  swimming  powers 
re  to  an  .'  npoi  .  i  ee  supplemental  to  its  inade- 


Flotation 


247 


«n 


quate  powers  of  flotation.  The  strokes  of  its  swim- 
ming antennae  are,  like  the  beating  of  our  own  hearts, 
intermittent  but  unceasing,  and  when  these  fail  it  falls 
to  its  grave  on  the  lake  bottom. 

Flotation  devices  usually  impede  free  swimming, 
especially  do  such  expansions  of  the  body  as  greatly 
increase  surface  contact  with  the  water.  It  is  in  the 
-resting  stages  of  animals,  therefore,  that  we  find  the 
best  development  of  floats:  such,  for  example,  as  the 
overwintering  statoblasts  of  the  Bryo- 
zoan,  Pectinatella,  shown  in  the  accom- 
panying figure.  Here  an  encysted  mass 
of  living  but  inactive  cells  is  sur- 
rounded by  a  buoyant,  air-filled  an- 
nular cushion,  as  with  a  life  preserver, 
and  floats  freely  upon  the  surface  of 
the  water,  and  is  driven  about  by  the 
waves. 

Too  great  buoyancy  is,  however,  as 
much  a  peril  to  the  active  micro-organ- 
isms of  the  water  as  too  little.  Contact 
with  the  air  at  the  surface  brings  to  soft 
protoplasmic  bodies,  the  peril  of  evap- 
oration. Entanglement  in  the  surface 
film  is  virtual  imprisonment  to  certain 
of  the  water-fleas,  as  we  shall  see  in 
the  next  chapter.  It  is  desirable  that 
they  should  live  not  on  but  near  the 
surface.  A  specific  gravity  about  that 
of  water  would  seem  to  be  the  optimum 
for  organisms  that  drift  passively  about:  a  little  greater 
than  that  of  water  for  those  that  sustain  themselves  in 
part  by  swimming. 

Terrestrial  creatures  like  ourselves;  who  live  on  the 
bottom  in  a  sea  of  air  with  s<  1  ground  beneath  our 
feet,  have  at  first  some  dime-         n  realizing  the  nicety 


Fig.  150.  The  over- 
wintering stage 
of  the  bryozoan, 
Pectinatella ;  a 
statoblast  or 
gemmule.  The 
central  portion 
contains  the  liv- 
ing cells.  The 
dark  ring  of  min- 
ute air-tilled  cells 
is  the  float.  The 
peripheral  an- 
chor-like pro- 
cesses are  attach- 
ment hooks  for 
securing  distribu- 
tion by  animals. 


248       Adjustment  to  Conditions  of  Aquatic  Life 

of  the  adjustment  that  keeps  a  whole  population  in  the 
water  afloat  near  to,  but  not  at  the  surface.  This  comes 
out  most  clearly,  perhaps,  in  those  minor  changes  of 
form  that  accompany  seasonal  changes  in  temperature 
of  the  water.  In  summer  when  the  viscosity  of  the 
water  grows  less  (and  when  in  consequence  its  resist  - 


Fig.  151.  Summer  and  winter  forms  of  plancton  animals:  sum- 
mer above,  winter  below,  a,  the  flagellate  Ceratium;  b,  the 
rotifer  Asplanchna;  c,  d,  e,  water-fleas;  c  and  d,  Daphne; 
e,  Bosmina.     (After  Wesenberg-Lund). 


ance  to  sinking  is  diminished)  the  surface  of  many 
planet  on  organisms  is  increased  to  correspond.  The 
slender  diatoms  grow  longer  and  slenderer,  the  spines 
on  certain  loricate  rotifers  grow  longer.  Bristles  and 
hairs  extend  and  plumes  and  fringes  grow  denser.  Even 
^e  form  of  the  body  is  altered  to  increase  surface- 
intact  with  th<.  WL-7.T.     A  few  examples  are  shown  in 


Swimming 


249 


the  accompanying  figures.  These  changes  when  fol- 
lowed thro  the  year  show  a  rather  distinct  correspond- 
ence to  the  seasonal  changes  in  viscosity  of  the  water. 


K-Jf-) 


Fig.  152.  Seasonal  form  changes 'of  the  water-flea,  Bosmina  coregoni.  The 
fractional  figures  above  indicate  date:  those  below  indicate  corresponding 
temperatures  in  °C.       (After  Wesenberg-Lund.) 

Swimming — For  rapid  locomotion  through  the  water 
there  are  numberless  devices  for  propulsion,  but  there 
is  only  one  thoroly  successful  form  of  body;  and  that 
is  the  so-called  "stream-line  form"  (fig. 
153).  It  is  the  form  of  body  of  a  fish: 
an  elongate  tapering  form,  narrowed 
toward  either  end,  but  sloping  more 
gently  to  the  rear.  It  is  also  the  form 
of  body  of  a  bird  encased  in  its  feathers. 
It  is  probably  the  form  of  body  best 
adapted  for  traversing  any  fluid  medium 
with  a  minimum  expenditure  of  energy. 
The  accompanying  diagram  explains  its 
efficiency.  The  white  arrow  indicates 
direction  of  movement.  The  gray  lines 
indicate  the  displacement  and  replace- 
ment of  the  water.  The  black  arrows 
indicate  the  direction  in  which  the 
forces  act.  At  the  front  the  force  of 
the  body  is  exerted  against  the  water; 
at  the  rear  the  force  of  the  water  is  exerted  against  lb 
body.      The   water,    being   perfectly   mobile,   returi 


Fig.  153.  Stream- 
line form.  For 
explanation  see 
text. 


250      Adjustment  to  Conditions  of  Aquatic  Life 

after  displacement;  and  much  of  the  force  expended 
in  pushing  it  aside  at  the  front  is  regained  by  the 
return-push  of  the  water  against  the  sloping  rearward 
portion  of  the  body. 

The  advantage  of  stream-line  form  is  equally  great 
whether  a  body  be  moving  through  still  water,  or 
whether  it  be  standing  against  moving  water.  A 
mackerel  swimming  in  the  sea  is  benefited  no  more  than 
is  a  darter  holding  its  stationary  position  on  the  stream 
bed.  To  this  we  shall  have  occasion  to  return  when 
discussing  the  rapid -water  societies. 

Apparatus  for  propulsion  is  endlessly  varied  in  the 
different  animal  groups.  Plants  have  developed  hardly 
any  sort  of  swimming  apparatus  beyond  cilia  and 
flagella.  These  also  serve  the  needs  of  many  of  the 
1<  >wer  animals — the  protozoa,  the  flat  worms,  the  roti- 
fers, trochophores  and  other  larvae,  sperm  cells  genera lly . 
etc.  But  more  widely  ranging  animals  of  larger  size 
have  developed  better  swimming  apparatus,  either  with 
or  without  appendages.  Snakes  swim  by  means  of 
horizontal  undulating  or  sculling  movements  of  the 
body,  and  so  also  do  many  of  the  common  minute 
Oligochaete  worms.  Horseleeches  swim  in  much  the 
same  manner,  save  that  the  undulations  of  the  body  are 
in  the  vertical  plane.  Midge  larvae  ("bloodworms") 
swim  with  figure-of-8-shaped  loopings  of  the  body  that 
are  quite  characteristic.  Mosquito  larvae  are 
"wrigglers,"  and  so  also  are  many  fly  and  beetle  larvae, 
tho  each  kind  wriggles  after  its  own  fashion.  Dragon- 
fly nymphs  swim  by  sudden  ejection  of  water  from  the 
rectal  respiratory  chamber. 

All  of  these  swim  without  the  aid  of  movable  appen- 
dages; but  the  laf  rer  animals  swim  by  means  of  special 
vrimming  organs,  fri  red  and  flattened  in  form  and 
aving  Wike  f    icti~n.     These  may  be  fins,  or 


Life  on  the  Bottom  251 


legs,  or  antennae,  or  gill  plates,  in  infinite   variety  of 
length,  form,  position  and  design. 

Great  is  the  diversity  in  aspect  and  in  action  of  the 
animals  that  swim.  Yet  it  is  perfectly  clear,  even  on  a 
casual  inspection,  that  the  best  swimmers  of  them  all  are 
those  that  combine  proper  form  of  body — stream-line 
form — with  caudal  propulsion  by  means  of  a  strong 
tail-fin. 

LIFE   ON   THE   BOTTOM 

Shoreward,  the  earth  beneath  the  waters  gives 
aquatic  organisms  an  opportunity  to  find  a  resting  place, 
a  temporary  shelter,  or  a  permanent  home.  Flotation 
devices  and  ability  at  swimming  may  yet  be  of  advan- 
tage to  the  more  free-ranging  forms;  but  the  existence 
of  possible  shelter  and  of  solid  support  makes  for  a  line 
of  adaptations  of  an  entirely  different  sort.  Here  dwell 
the  aquatic  organisms  that  have  acquired  heavy  armor 
for  defense;  heavy  shells,  as  in  the  mussels;  heavy 
carapaces  as  in  the  crustaceans ;  heavy  chitinous  armor 
as  in  the  insects ;  or  heavy  incrustations  of  lime  as  in  the 
stone  worts. 

The  condition  of  the  bottom  varies  from  soft  ooze  in 
still  water  to  bare  rocks  on  wave  washed  shores.  The 
differences  are  very  great,  and  they  entail  significant 
differences  in  the  structure  of  corresponding  plant  and 
animal  associations.  These  have  been  little  studied 
hitherto,  but  a  few  of  the  more  obvious  adaptations  to 
bottom  conditions  may  be  pointed  out  in  passing. 

First  we  will  note  some  adaptations  for  avoidance  of 
smothering  in  silt  on  soft  bottoms;  then  some  adapta- 
tions for  finding  shelter  by  burrowing  in  sandy  bottoms 
and  by  building  artificial  defenses:  then  some  adapta- 
tions for  withstanding  the  wash  of  die  current  on  hard 
bottoms. 

.    1  7.  i*»0 


252      Adjustment  to  Conditions  of  Aquatic  Life 


I 
Avoidance  of  silt — -Gills  are  essentially  thin-walled 
expansions  of  the  body,  that  provide  increased  surface 
for  contact  with  the  water,  and  thus  promote  that 
exchange  of  gases  which  we  call  respiration.  Gills 
usually  develop  on  the  outside  of  the  body;    for  it  is 

only  in  contact  with  the  water 
that  they  can  serve  their  func- 
tion. In  most  animals  that  live 
in  clear  waters  they  are  freely 
exposed  upon  the  outside;  but 
in  animals  that  live  on  soft 
muddy  bottoms  they  are  with- 
drawn into  protected  chambers 
(or,  rather,  sheltered  by  the 
outgrowth  of  surrounding  parts) 
and  fresh  water  is  passed  to 
them  thro  strainers.  Thus  the 
gills  of  a  crawfish  occupy  capa- 
cious gill  chambers  at  the  sides 
of  the  thorax,  and  water  is 
admitted  to  them  thro  a  set 
of  marginal  strainers.  The  gills 
of  fresh -water  mussels  are  located 
at  the  rear  of  the  foot  within  the 
inclosure  of  valves  and  mantle, 
and  water  is  passed  to  and  from 
them  thro  the  siphons.  The  gills 
of  dragonfly  nymphs  are  located 
on  the  inner  walls  of  a  rectal 
respiratory  chamber,  and  water  to  cover  them  is  slowly 
drawn  in  thro  a  complicated  strainer  that  guards  the 
anal  aperture,  and  then  suddenly  expelled  thro  the 
same  opening,  the  valves  swinging  freely  outward. 

*  There  is  proba  )ly  no  better  illustration  of  parallel 
adaptation  for>s^     avoidance  ^haa^that  furnished  by  the 


Fig  154.  The  abdomen  of 
Asellus,  inverted,  showing 
gill  packets. 


Avoidance  of  Silt 


253 


crustacean,  Asellus,  and  the  nymph  of  the  mayfly, 
Caenis.  Both  live  in  muddy  bottoms  where  there  is' 
much  fine  silt.  Both  possess  paired  plate-like  gills. 
In  Asellus  they  are  developed  underneath  the  abdomen ; 
in  Caenis  upon  the  back.  In  Asellus  they  are  double; 
in  Caenis,  simple.  In 
Asellus  they  are  blood 
gills;  in  Caenis,  tracheal 
gills.  In  both  they  are 
developed  externally  in 
series,  a  pair  correspond- 
ing to  a  body  segment. 
In  both  they  are  soft  and 
white  and  very  delicate. 
But  in  both  an  anterior 
pair  has  been  developed 
to  form  a  pair  of  enlarged 
opercula  or  gill  covers. 
These  are  concave  pos- 
teriorly and  overlie  and 
protect  the  true  gills. 
The  gills  have  been  ap- 
proximated more  closely, 
so  that  they  are  the  more 
readily  covered  over ;  and 
they  have  developed  in- 
terlacing fringes  of  radi-  f 
ating  marginal  hairs, 
which   act    as    strainers, 

when  the  covers  are   raised   to   open  the  respiratory 
chamber. 

Such  are  the  mechanical  means  whereby  suffocation 
in  the  mud  is  avoided.     It  must  not  be  overlooked  that 
there  is  a  physiological  adaptation  to  the  same  end.     A 
number  of  soft  bodied  thin-skinr  d  iniimls  haw 
unusual  amount  of  ha^op^^n  '•     h    bl         plasm. 


The    nymph  of   the  mayfly 
Casnis,  showing  dorsal  gill  packets. 


254       Adjustment  to   Conditions  of  Aquatic  Life 

enough,  indeed,  to  give  them  a  bright  red  color.  This 
substance  has  a  great  capacity  for  gathering  up  oxygen 
where  the  supply  is  scanty,  and  of  yielding  it  over 
to  the  tissues  as  needed.  True  worms  that  burrow  in 
deep  mud,  and  Tubifex  (see  fig.  83  on  p.  174)  that  bur- 
rows less  deeply  and  the  larger  bright  red  tube  making 
larvae  of  midges  known  as  "blood  worms"  (see  fig.  236 
on  p.  393)  are  examples.  Since  these  forms  live  in  the 
softest  bottoms,  where  the  supply  of  oxygen  is  poorest, 
where  few  other  forms  are  able  to  endure  the  conditions, 
their  way  of  getting  on  must  be  of  considerable  efficiency. 

II 

Burrowing — The  ground  beneath  the  water  offers 
protection  to  any  creature  that  can  enter  it ;  protection 
from  observation  to  a  bottom  sprawler,  that  lies  littered 
over  with  fallen  silt;  protection  from  attack  about  in 
proportion  to  its  hardness,  to  anything  that  can  bur- 
row. 

Animals  differ  much  in  their  burrowing  habits  and  in 
the  depth  to  which  they  penetrate  the  bottom.  Many 
mussels  and  snails  burrow  very  shallowly,  push- 
ing their  way  along  beneath  the  surface,  the  soft  foot 
covered,  the  hard  shell-armored  back  exposed.  The 
nymphs  of  Gomphine  dragonflies  (fig.  116  on  p.  209) 
burrow  along  beneath  the  bottom  with  only  the  tip 
of  the  abdomen  exposed  at  the  surface  of  the  mud. 
Other  insect  larvae  descend  more  deeply  into  burrows 
which  remain  open  to  the  water  above:  while  horsefly 
larvae  and  certain  worms  descend  deeply  into  soft  mud. 

The  two  principal  methods  by  which  animals  open 
passageways  thro  the  bottom  are  (1)  by  digging,  and 
(2)  by  squeezing  thro.  Digging  is  the  method  most 
familiar  to  us,  it  being  commonly  used  by  terrestrial 
an^mils.  Squeezing  thro  is  the  comn  *st  m<  ^  -»f 
ac  uatic  burrowe  :s.    +  . 


Burro 


wing 


?55 


Fig.    156.     A  nymph  of  a    burrowing  mayfly,  Ephemera.       (From   Annals 
Entom.  Soc.  of  America:     drawing  by  Anna  H.  Morgan). 

The  digging  of  burrows  requires  special  tools  for  mov- 
ing the  earth  aside.  These,  as  with  land  animals,  are 
usually  flattened  and  shovel-like  fore  legs.  The  other 
legs  are  closely  appressed  to  the  body  to  accommodate 
them  to  the  narrow  burrow.  The  hind  legs  are  directed 
backward.  The  head  is  usually  flattened  and  more  or 
less  wedge-shaped,  and  often  specially  adapted  for 
lifting  up  the  soil  preparatory  to  advancing  thro  it 
(see  fig.  116  on  p.  209). 

One  of  the  best  exponents  of  the  burrowing  habit  is 
the  nymph  of  the  may- 
fly, Hexagenia,  whose 
innumerable  tunnels 
penetrate  the  beds  of 
all  our  larger  lakes  and 
rivers.  It  is  an  un- 
gainly creature  when 
exposed  in  open  water; 
but  when  given  a  bed 
of  sand  to  dig  in,  it 
shows  ;ts  fitness.  Be- 
sir1    5         ving        ^t     that 

aside 


Fig.  157.  The  front  of  a  burrowing  may- 
fly nymph,  Hexagenia,  much  enlarged, 
showing  the  pointed  head,  the  great 
mandibular    tusks    and    the    Battened 

fore  legs. 

are    ad-nirably    fitter*' '  £>r 
it  has  a  p  l'r  of  enormors 


256      Adjustment  to  Conditions  of  Aquatic  Life 

mandibular  tusks  projecting  forward  from  beneath 
the  head.  It  thrusts  forward  its  approximated  blade- 
like fore  feet,  and  with  them  scrapes  the  sand 
aside,  making  a  hole.  Then  it  thrusts  its  tusks  into 
the  bottom  of  the  hole  and  lifts  the  earth  forward  and 
upward.  Then,  moving  forward  into  the  opening 
thus  begun  and  repeating  these  operations,  it  quickly 
descends  from  view. 

Squeezing  thro  the  bottom  is  the  method  of  progress 
most  available  to  soft-bodied  animals.  Those  lacking 
hard  parts  such  as  shovels  and  tusks  with  which  to  dig 
make  progress  by  pushing  a  slender  front  into  a  narrow 
opening,  and  then  distending  and,  by  blood  pressure 
enlarging  the  passageway.  The  horsefly  larva  shown  in 
figure  137  on  page  230  (discussed  on  page  227)  is  a  good 
example.  The  body  is  somewhat  spindle-shaped,  taper- 
ing both  ways,  and  adapted  for  traveling  forward  or 
backward.  It  is  exceedingly  changeable  in  proportions 
being  adjustable  in  length,  breadth  and  thickness. 
Indeed,  the  whole  interior  is  a  moving  mass  of  soft 
organs,  any  one  of  which  may  be  seen  thro  the  trans- 
parent skin,  slipping  backward  or  forward  inside  for  a 
distance  of  several  segments.  The  body  wall  is  lined 
with  strong  muscles  inside,  and  outside  it  bears  rings 
of  stout  tubercles,  which  may  be  drawn  in  for  passing, 
or  set  out  rigidly  to  hold  against  the  walls  of  the  burrow. 
The  extraordinary  adjustability  of  both  exterior  and 
interior  is  the  key  to  its  efficiency.  When  such  a  larva 
wishes  to  push  forward  in  the  soil,  it  distends  and  sets 
its  tubercles  in  the  rear*  to  hold  against  the  walls,  and 
drives  the  pointed  head  forward  full  length  into  the  mud ; 
then  it  compresses  the  rear  portion,  forcing  the  blood 


*/r£rtam  cranefly  larvae  (such  as  Pedicia  albivitta  and  liriocera  spinosa)  that 
live  Is  of  gravel  have  one  segment  near  the  end  of  the  body  expansible  to 

air.       .  balloon-like  proportions,  forming  a  veritable  pushing-ring  in  the  rear. 


Shelter  Building 


:0/ 


forward  to  distend  the  body  there,  thus  widening  the 
burrow.  And  if  anyone  would  see  how  such  a  larva  gets 
through  a  narrow  space  when  the  walls  cannot  be 
pushed  farther  apart,  let  him  wet  his  hand  and  close  the 
larva  in  its  palm ;  the  larva  will  quickly  slip  out  between 
the  ringers  of  the  tightly  closed  hand;  and  when  half 
way  out  it  will  present  a  strikingly  dunfb-bell-shaped 
outline.  Here,  again,  we  see  the  advantage  of  its 
almost  fluid  interior. 

This  adjustability  of  body,  is  of  course,  not  peculiar  to 
soft  bodied  insect  larvas ;  it  is  seen  in  leeches  and  slugs 
and  many  worms. 

The  mussel's  mode  of  burrowing  is  not  essentially 
different  from  that  above  described.  The  slender 
hollow  foot  is  pushed  forward  into  the  sand,  and  then 
distended  by  blood  forced  into  it  from  the  rear.  When 
sufficiently  distended  to  hold  securely  by  pressure 
against  the  sand,  a  strong  pull  drags  the  heavy  shell 
forward. 

Ill 

Shelter  building — Some  animals  produce  adhesive 
secretions  that  harden  on  contact  with  the  water. 
Thus,  these  are  able  to  bind  loose  objects  together  into 
shelters  more  suitable  for  their  residence  than  any  that 
nature  furnishes  ready  made.  The  habit  of  shelter 
building  has  sprung  up  in  many  groups;  in  such 
protozoans  as  Difflugia  (see  fig.  69  c  on  p.  39) ;  in  such 
worms  as  Dero  (see  fig.  82  on  p.  174);  in  such  rotifers 
as  Melicerta  (see  fig.  86  on  p.  178) ;  in  such  caterpillars 
as  Hydrocampa  (see  fig.  127  on  p.  219);  in  nearly  all 
midges,  as  Chironomus  (see  figure  134  on  p.  22u)  and 
Tanytarsus  (see  fig.  223  on  p.  373);  and  especially  in 
the  caddis- worms,  all  of  which  construct  shelters  of  some 
sort  and  most  of  which  build  portable  cases.  n.he 
extraordinary  prevalence  in  all  fresh  waters  of  such  * ;     is 


258       Adjustment  to  Conditions  of  Aquatic  Life 


as  the  larvae  of  midges  and  caddis-flies  would  indicate 
that  the  habit  has  been  biologically  profitable. 

According  to  Betten  the  habit  probably  began  with 
the  gathering  and  fastening  together  of  fragments  for  a 
fixed  shelter,  and  the  portable,  artifically  constructed, 
silk  lined  tubes  of  the  higher  caddis-worms  are  a  more 
recent  evolution. 

IV 

Withstanding  the  wash  of  moving  waters — Where 
waters  rush  swiftly,  mud  and  sand  and  all  loose  shelters 


Fig.  158.  Stone  from  a  brook  bed,  bearing  tubes  of  midge 
larvae  and  portable  cases  of  two  species  of  caddis- worms. 
The  more  numerous  spindle-shaped  cases  are  those  of 
the  micro-caddisworms  of  the  genus  Hydroptila.  For 
more  distinct  midge  tubes  see  figs.  134  and  223. 

are  swept  away.  Only  hard  bare  surfaces  remain,  and 
the  creature  that  finds  there  a  place  of  residence  must 
build  its  own  shelter,  or  must  possess  more  than  ordi- 
nary advantages  for  maintaining  its  place.  The  gifts  of 
the  gods  to  those  that  live  in  such  places  are  chiefly 
these  three: 

1.  Ability  to  construct  flood-proof  shelters.  Such 
are  the  fixed  cases  of  the  caddis-worms  and  midge  larvae 
(ft*.  158)  to  whic1  ^all  give  further  consideration  in 
the  next    %~ 


Withstanding  the  Wash  of  Moving  Waters      259 


2.  Special  organs  for  hanging  on  to  water- swept 
surfaces.  Such  organs  are  the  huge  grappling  claws  of 
the  nymphs  of  the  larger  stonenies  (see  fig.  11 1  on  p. 
204)  and  of  the  riffle  beetles:  also  powerful  adhesive 
suckers,  such  as  those  of  the  larvae  of  the  net -winged 

midges. 

3.  Form  of  body  that 
diminishes  resistance  to 
flow  of  the  water.  This 
we  have  already  seen  is 
stream-line  form.  In 
our  discussion  of  swim- 
ming we  pointed  out 
that  the  form  of  body 
that  offers  least  resist- 
ance to  the  progress  of 
the  body  through  the 
water  will  also  offer  least 
resistance  to  the  flow  of 
water  past  the  body.  So 
we  find  the  animals  that 
stand  still  in  running 
water  are  of  stream-line 
form ;  darters  and  other 
fishes  of  the  rapids ;  may- 
flies, such  as  Siphlon- 
urus  and  Chirotenetes ; 
even  such  odd  forms  as  the  larvae  of  Simulium,  which 
hangs  by  a  single  sucker  suspended  head  downwards  in 
the  stream.  Indeed,  the  case  of  Simulium  is  especially 
significant,  for  with  the  reversal  of  the  position  of  the 
body  the  greater  widening  of  the  body  is  shifted  from 
the  anterior  to  the  posterior  end,  and  stream-line  form 
is  preserved.  Such  forms  as  these  live  in  the  open, 
remain  for  the  most  part  quietly  in  one  position  and 
wait  for  the  current  to  bring  their  food  to  t>  m. 


Fig.  159.  The  larva  of  the  net- 
winged  midge,  Blepharocera,  dorsal 
and  ventral  views. 


260       Adjustment  to  Conditions  of  Aquatic  Life 


.r'Y 


i 


\C*'' 


Fi 


animals. 


Limpet-shaped 
At  right  the  larva 
of  the  Parnid  beetle,  Pse- 
phenus,  known  as  the 
"water-penny."  At  left, 
the  snail,  Ancvlus. 


There  are  other  more  numerous  forms  living  in  rapid 
water  that  cling  closer  to  the  solid  surfaces,  move  about 
upon  and  forage  freely  on  these  surfaces,  and  the 
adaptations  of  these  are  related  to  the  surfaces  as  much 

as  to  the  open  stream.  These 
have  to  meet  and  withstand  the 
water  also,  but  only  on  one  side; 
and  the  form  is  half  of  that  of 
our  diagram  (fig.  1 53) .  It  is  that 
figure  divided  in  the  median 
vertical  plane,  with  the  flat  side 
then  applied  to  the  supporting 
surface,  and  flattened  out  a  bit  at 
the  edges.  This  is  not  fish  form, 
but  it  is  the  form  of  a  limpet. 
This  is  the  form  taken  on  by  a 
majority  of  the  animals  living  in  rapid  waters.  When 
the  legs  are  larger  they  fall  outside  of  the  figure,  as  in 
the  mayfly  shown  on  page  367,  and 
are  flattened  and  laid  down  close 
against  the  surface  so  as  to  present  only 
their  thin  edges  to  the  water.  When 
the  legs  are  small,  as  in  the  water- 
penny,  (fig.  160)  they  are  covered  in 
underneath.  Sometimes  there  are  no 
legs,  as  in  the  flatworms,  and  in  the 
snail,  Ancylus. 

Here,  surely,  we  have  the  impress 
of  environment.  Many  living  beings 
of  different  structural  types  are  mould- 
ed to  a  common  form  to  meet  a  com- 
mon need;  and  even  the  non-living 
shelters  built  by  other  animals  are 
fashioned  to  the  same  form.  The  case 
of  the  micro-caddisworm,  Ithytrichia 
confusa  (fig.  161)  is  also  limp^  -'  aaped; 


Fig 


161.  The  larva 
of  the  caddis- worm, 
Ithytrichia  confusa. 


Adjustment  of  the  Life  Cycle  261 


so  also  is  the  pupal  shelter  of  the  caterpillar  of  Etophila 
fulicalis;  hardly  less  so  is  the  portable  case  of  the  larva 
of  the  caddis-fly,  Leptocerus  ancylus  or  of  Molanna 
angustata. 

ADJUSTMENT  OF  THE   LIFE   CYCLE 

Life  runs  on  serenely  in  the  depths  of  the  seas  where, 
as  we  have  noted  in  Chapter  II,  there  is  no  change  of 
season;  but  in  shoal  and  impermanent  waters  it  meets 
with  great  vicissitudes.  Winter's  freezing  and  summer's 
drouth,  exhaustion  of  food  and  exclusion  of  light  and  of 
air,  impose  hard  conditions  here.  Yet  in  these  shoals 
is  found  perhaps  the  world's  greatest  density  of  popula- 


Fig.  162.  The  flattened  and  limpet-shaped  cases  of  Ithytrichia 
confusa,  as  they  appearr.  attached  to  the  surface  of  a  sub- 
merged stone. 


262      Adjustment  to   Condition   of  Aquatic  Life 

tion.  Here  competition  for  food  and  standing  room  is 
most  severe.  And  here  are  made  some  of  the  most 
remarkable  shifts  for  maintaining  "a  place  in  the  sun." 

Encystment — The  shifts  which  we  are  here  to  consider 
are  those  made  in  avoidance  of  the  struggle — shifts 
which  have  to  do  with  the  tiding  over  of  unfavorable 
seasons  by  withdrawal  from  activity.  This  means 
encystment  or  encasement  of  some  sort  or  in  some 
degree.  The  living  substance  secretes  about  itself 
some  sort  of  a  protective  layer,  and,  enclosed  within  it, 
ceases  from  all  its  ordinary  functions. 

This  is  the  most  familiar  to  us  in  the  reproductive 
bodies  of  plants  and  animals;  in  the  zygospores  of 
Spirogyra  and  desmids  and  other  conjugates;  in  the 
fruiting  bodies  of  the  stoneworts;  in  the  seeds  of  the 
higher  plants;  and  in  the  over-wintering  eggs  of  many 
animals.  Most  remarkable  perhaps  is  the  brief  seasonal 
activity  of  forms  that  inhabit  temporary  pools.  Such 
Branchipods  as  Chirocephalus  (see  fig.  90  on  p.  184) 
Estheria  and  Apus,  appear  in  early  spring  in  pools 
formed  from  melting  snow.  They  run  a  brief  course  of 
a  few  weeks  of  activity,  lay  their  eggs  and  disappear  to 
be  seen  no  more  until  the  snows  melt  again.  Their 
eggs  being  resistant  to  both  drying  and  freezing,  are 
able  to  await  the  return  of  favorable  conditions  for 
growth.  The  eggs  of  Estheria  have  been  placed  in 
water  and  hatched  after  being  kept  dry  for  nine  years. 
But  it  is  not  alone  reproouctive  bodies  that  thus  tide 
over  unfavorable  periods.  The  flatworm,  Planar ia 
velata,  divides  itself  into  pieces  which  encyst  in  a  layer 
of  slime  and  thus  await  the  return  of  conditions  favor- 
able for  growth.  The  copepod,  Cyclops  bicuspidatus, 
according  to  Birge  and  Juday  (09)  spends  the  summer 
in  a  sort  of  cocoon  composed  of  mud  and  other  bottom 
materials  rather  firmly  cemented  together  about  its 


Encystment 


263 


body.  It  forms  this  cocoon  about  the  latter  end  of 
May.  It  reposes  quietly  upon  the  bottom  during  the 
entire  summer — thro  a  longer  period,  indeed,  than 
that  of  absence  of  oxygen  from  the  water.  Hatch- 
ing and  resumption  of  activity  begin  in  September  and 
continue  into  October.  Marsh  (09)  suggests  that 
with  us  this  species  "may  be  considered  preeminently  a 


Fig.  163.     Hibernacula  of  the  common  bladderwort. 


winter  form."     It  is  active  in  summer  only  in  cold 
mountain  lakes. 

The  over-wintering  buds  (hibernacula)  of  some  aquat- 
ic seed  plants  are  among  the  simplest  of  these  devices. 
Those  of  the  common  bladderwort  are  shown  in  figure 
1 63 .  At  the  approach  of  cold  weather  the  bladderwort 
ceases  to  unfold  new  leaves,  but  develops  at  the  tip  of 
each  branch  a  dense  bud  composed  of  close-laid  incom- 
pletely developed  leaves.  This  is  the  hibernaculum. 
It  is  really  an  abbreviated  and   undeveloped  branch. 


264      Adjustment  to  Conditions  of  Aquatic  Life 

Unlike  other  parts  of  the  plant,  its  specific  gravity  is 
greater  than  that  of  water.  It  is  enveloped  only  by  a 
thin  gelatinous  covering.  With  its  development  the 
functional  activity  of  the  old  plant  ceases ;  the  leaves 
lose  chlorophyl;    their  bladders  fall  away;    the  tissues 


Fig.  164.  The  remains  of  a  fresh- water  sponge  that  has 
grown  upon  a  spray  of  water-weed.  The  numerous 
rounded  seed-like  bodies  embedded  in  the  disintegrating 
tissue  are  statoblasts.     See  text. 

disintegrate;  and  finally  the  hibernacula  fall  to  the 
bottom  to  pass  the  winter  at  rest.  When  the  water 
begins  to  be  warmer  in  spring,  the  buds  resume  growth, 
the  axis  lengthens,  the  leaves  expand,  air  spaces 
develop  and  gases  fill  them,  buoying  the  young  snoots 
up  into  better  light,  and  the  activities  of  another  season 
are  begun. 


Winter  Eggs  26- 


Statoblasts — Perhaps  the  most  specialized  of  over- 
wintering bodies  are  those  of  the  Bryozoans  and  fresh- 
water sponges,  known  as  statoblasts.  These  are  little 
masses  of  living  cells  invested  with  a  tough  and  hard 
and  highly  resistent  outer  coat.  They  are  formed 
within  the  flesh  of  the  parent  animal  (as  indicated  for 
Bryozoan  in  fig.  yj  on  p.  167),  and  are  liberated  at  its 
dissolution  (as  indicated  for  a  sponge  in  the  accompany- 
ing figure) .  ^  They  alone  survive  the  winter.  As  noted 
earlier  in  this  chapter,  their  chitinous  coats  are  often 
expanded  with  air  cavities  to  form  efficient  floats: 
sometimes  in  Bryozoan  statoblasts  there  is  added  to 
this  a  series  of  hooks  for  securing  distribution  by  ani- 
mals (see  fig.  150  on  p.  247).  Often  in  autumn  at  the 
Cornell  Biological  Field  Station  collecting  nets  become 
clogged  with  these  hooked  statoblasts. 

In  the  fresh-water  sponges  the  walls  of  the  statoblast 
are  stiffened  with  delicate  and  beautiful  siliceous 
spicules,  and  there  is  at  one  side  a  pore  through  which 
the  living  cells  find  exit  at  the  proper  season.  Since 
marine  sponges  lack  statoblasts,  and  some  fresh-water 
species  do  not  have  them,  it  is  probable  that  they  are 
an  adaptation  of  the  life  cycle  to  conditions  imposed 
by  shoal  and  impermanent  waters. 

Winter  Eggs — Another  seasonal  modification  of  the 
life  cycle  is  seen  in  the  Rotifers  and  water-fleas.  Here 
there  are  produced  two  kinds  of  eggs;  summer  eggs 
that  develop  quickly  and  winter  eggs  that  hibernate. 
The  summer  eggs  for  a  long  period  produce  females 
only.  They  develop  without  fertilization.  In  both 
these  groups  males  are  of  very  infrequent  occurrence. 
They  appear  at  the  end  of  the  season.  The  last  of  the 
line  of  parthenogenetic  females  produce  eggs  from  which 
hatch  both  males  and  females  and  the  last  crop  of  eggs 
is  fertilized.     These  are  the  over-wintering  eggs. 


266      Adjustment  to   Conditions  of  Aquatic  Life 

The  accompanying  figures  illustrate  both  kinds  of 
eggs  in  the  water-flea,  Ceriodaphnia,  an  inhabitant  of 
bottomland  ponds.  Figure  165  shows  a  female  with 
the  summer  eggs  in  the  brood  chamber  on  her  back. 
These  thin-shelled  eggs  are  greenish  in  color.  They 
hatch  where  they  are  and  the  young  Ceriodaphnias  live 


Fig.  165.     Ceriodaphnia,  with  summer  e£ 


within  the  brood-chamber  until  they  have  absorbed  all 
the  yolk  stored  within  the  egg  and  have  become  very 
active.  Then  they  escape  between  the  valves  of  the 
shell  at  the  rear. 

Winter  eggs  in  this  species  are  produced  singly. 
Figure  1 66  shows  one  in  the  brood  chamber  of  another 
female.     It  is  inclosed  in  a  chitinized  protective  cover- 


Winter  Eggs 


267 


ing,  which,  because  of  its  saddle-shaped  outline,  is  called 
an  ephippium.  This  egg  is  liberated  unhatched  by  the 
molting  of  the  female,  as  shown  in  figure  167.  It 
remains  in  its  ephippium  over  winter,  protected  from 
freezing,   from  drouth   and   from   mechanical  injury, 


Fig.  166. 


Ceriodaphnia  bearing  an  ephippium  containing  the 
single  winter  egg. 


and  buoyed  up  just  enough  to  prevent  deep  sub- 
mergence in  the  mud  of  the  bottom.  With  the  return 
of  warmer  weather  it  may  hatch  and  start  a  new 
line  of  parthenogenetic  female  Ceriodaphnias. 

Thus,  it  is  that  many  organisms  are  removed  from  our 
waters  during  a  considerable  part  of  the  winter  season. 


268       Adjustment  to  Conditio)! s  of  Aquatic  Life 

The  water-fleas  and  many  of  our  rotifers  are  hibernating 
as  winter  eggs.  The  bryozoans  and  sponges  are  hiber- 
nating as  statoblasts.  Doubtless  many  of  the  simpler 
organisms  whose  wTays  are  still  unknown  to  us  have  their 


Fig.  167.  Ceriodaphnia,  molted  skin  and  liberated  ephippium 
of  the  same  individual  shown  in  the  preceding  figure.  This 
photograph  was  taken  only  a  few  minutes  after  the  other. 
The  female  after  molting  immediately  swam  away. 

own  times  and  seasons  and  modes  of  passing  a  period  of 
rest.  It  is  doubtless  due,  also,  to  the  ease  and  safety 
with  which  they  may  be  transported  when  in  such 
condition  that  they  all  have  a  wide  distribution  over  the 
face  of  the  earth.     In  range,  they  are  cosmopolitan. 


Readaptation  to  Life  in  the  Water  269 

Readaptations  to  life  in  the  water — The  more  primitive 
groups  of  aquatic  organisms  have,  doubtless,  always 
been  aquatic;  but  the  aquatic  members  of  several  of 
the  higher  groups  give  evidence  of  terrestrial  ancestry. 
Among  the  reasons  for  believing  them  to  have  devel- 
oped from  forms  that  once  lived  on  land  is  the  possession 
of  characters  that  could  have  developed  only  under 
terrestrial  conditions,  such  as  the  stomates  for  intake  of 
air  in  the  aquatic  vascular  plants,  the  lungs  of  aquatic 
mammals,  and  the  tracheae  and  spiracles  of  aquatic 
insects.  Furthermore,  they  are  but  a  few  members 
(relatively  speaking)  of  large  groups  that  remain 
predominantly  terrestrial  in  habits,  and  there  are  among 
them  many  diverse  forms,  fitted  for  aquatic  life  in  very 
different  ways,  and  showing  many  signs  of  independent 
adaptation. 

I 

The  vascular  plants  are  restricted  in  their  distribution 
to  shores  and  to  shoal  waters.  They  are  fitted  for 
growth  in  fixed  position  and  they  possess  a  high  degree 
of  internal  organization  with  a  development  of  vessels 
and  supporting  structures  that  cannot  withstand  the 
beating  of  heavy  waves.  As  compared  with  the  land 
plants  of  the  same  groups,  these  are  their  chief  structural 
characteristics : 

1.  In  root: — reduced  development.  With  submer- 
gence there  is  less  need  of  roots  for  food-gathering,  since 
absorption  may  take  place  over  the  entire  surface. 
Roots  of  aquatic  plants  serve  mainly  as  anchors ;  in  a 
few  floating  plants  as  balancers;  sometime  they  are 
entirely  absent. 

2.  In  stems: — many  characteristics,  chief  of  which 
are  the  following: 

a.     Reduction  of  water-carrying  tubes,  for  the  ob- 
vious reason  that  water  is  everywhere  available 


270      Adjustment  to  Conditions  of  Aquatic  Life 

b.  Reduction  of  wood  vessels  and  of  wood  fibers 
and  other  mechanical  tissues.  In  the  denser 
medium  of  the  water  these  are  not  needed,  as 
they  are  in  the  air,  to  support  the  body.  Pliancy, 
not  rigidity,  is  required  in  the  water. 

c.  Enlargement  of  air  spaces.  This  is  prevalent 
and  most  striking.  One  may  grasp  a  handful 
of  any  aquatic  stems  beneath  the  water  and 
squeeze  a  cloud  of  bubbles  out  of  them. 

d.  Concentration  of  vessels  near  the  center  of 
the  stem  where  they  are  least  liable  to  injury 
by  bending. 

e.  A  general  tendency  toward  slenderness  and 
pliancy  in  manner  of  growth,  brought  about 
usually  by  elongation  of  the  internodes. 

3.     In  leaves: — many  adaptive  characters;    among 
them  these: 

a.  Thinness  of  epidermis,  with  absence  of  cuticle 
and  of  ordinary  epidermal  hairs.  This  favors 
absorption  through  the  general  surfaces. 

b.  Reduction  of  stomates,  which  can  no  longer 
serve  for  intake  of  air. 

c.  Development  of  chlorophyl  in  the  epidermis, 
which,  losing  the  characters  which  fit  it  for 
control  of  evaporation,  takes  on  an  assimilatory 
function. 

d.  Isolateral  development,  i.  e.,  lack  of  differ- 
entiation between  the  two  surfaces. 

e.  Absence  of  petioles. 

/.  Alteration  of  leaf  form  with  two  general  ten- 
dencies manifest:  Those  growing  in  the  most 
stagnant  waters  become  much  dissected  (blad- 
derworts,  milfoils,  hornworts,  crowfoots,  etc.). 

Those  growing  in  the  more  open  and  turbu- 
lent waters  become  long,  ribbonlike,  and  very 
flexible  (eelgrass,  etc.). 


Re  adaptations  to  Life  in  the  Water  271 


In  general,  the  following  characteristics: 

a.  The  production  of  abundance  of  mucilage, 
which,  forming  a  coating  over  the  surface,  may 
be  of  use  to  the  plants  in  various  ways : 

1.  For  notation,  when  the  mucilage  is  of  low 
specific  gravity. 

2.  For  defense  against  animals  to  which  the 
mucilage  is  inedible  or  repugnant. 

3.  For  lubrication:  a  very  important  need; 
for,  when  crossed  plant  stems  are  tossed  by 
waves,  the  mucilage  reduces  their  mutual 
friction  and  prevents  breaking. 

4.  For  preventing  evaporation  on  chance  ex- 
posure to  the  air. 

5.  For  regulating  osmotic  pressure,  and  aiding 
in  the  physical  processes  of  metabolism. 

b .  Development  of  vegetative  reproductive  bodies : 

1.  Hibernacula,  such  as  those  of  the  bladder- 
wort  (fig.  162). 

2.  Tubers  such  as  those  of  the  sago  pondweed 
(see  fig.  228),  the  arrow-head,  etc. 

3.  Burs,  such  as  terminate  the  leafy  shoots  of 
the  rufned  pondweed  (see  fig.  63). 

4.  Offsets  and  runners,  such  as  are  common 
among  land  plants. 

5.  Detachable  branches  and  stem  segments, 
that  freely  produce  adventitious  roots  and 
establish  new  plants. 

c.  Diminished  seed  production.    This  is  correlated 

with  the  preceding.  Some  aquatics  such  as 
duckweeds  and  hornworts  are  rarely  known  to 
produce  seeds;  others  ripen  seeds,  but  rarely 
develop  plants  from  them.  Their  increase  is 
by  means  of  the  vegetative  propagative  struc- 
tures above  mentioned,  and  they  hold  their 
place  in  the  world  by  continuous  occupation 
of  it. 


272      Adjustment  to  Conditions  of  Aquatic  Life 


II 

The  mammals  that  live  in  the  water  are  two  small 
orders  of  whales,  Cetacea  and  Sirenia,  and  a  few 
scattering  representatives  of  half  a  dozen  other  orders. 
Tho  few  in  number  they  represent  almost  the  entire 
range  of  mammalian  structure.  They  vary  in  their 
degree  of  fitness  for  water  life  from  the  shore-haunting 
water-vole,  that  has  not  even  webbing  between  its  toes, 
to  the  ocean  going  whales,  of  distinctly  fish-like  form, 
that  are  entirely  seaworthy.  It  is  a  fine  series  of 
adaptations  they  present. 

For  all  land-animals,  returned  to  the  water  to  live, 
there  are  two  principal  problems,  (i)  the  problem  of 
getting  air  and  (2)  the  problem  of  locomotion  in  the 
denser  medium.  Warm-blooded  animals  have  also 
the  problem  of  maintaining  the  heat  of  the  body  in 
contact  with  the  water.  To  begin  with  the  point  last 
named,  aquatic  mammals  have  solved  the  problem  of 
heat  insulation  by  developing  a  copious  layer  of  fat  and 
oils  underneath  the  skin.  This  development  culminates 
in  the  extraordinary  accumulation  of  blubber  in  arctic 
whales. 

No  aquatic  mammals  have  developed  gills.  They  all 
breathe  by  means  of  lungs  as  did  their  terrestrial  ances- 
tors. All  must  come  to  the  surface  for  air.  Their 
respiratory  adaptations  are  slight,  consisting  in  the 
shifting  of  the  nostrils  to  a  more  dorsal  position  and 
providing  them  with  closable  flaps  or  valves,  to  prevent 
ingress  of  the  water  during  submergence. 

It  is  with  reference  to  aquatic  locomotion  that 
mammals  show  the  most  striking  adaptations.  About 
in  proportion  to  their  fitness  for  life  in  the  water  they 
approximate  to  the  fish-like  contour  of  body  that  we 
have  already  discussed  (page  249)  as  stream-like  form. 
Solidity  and  compactness  of  the  anterior  portion  of  the 


Aquatic  Adaptations  of  Insects  273 

body  are  brought  about  by  consolidation  of  the  neck 
vertebrae  and  shortening  of  the  cranium.  Smoothness 
of  contour,  (and  therefore  diminished  resistance  to 
passage  through  the  water)  is  promoted  by  (1)  the  loss 
of  hair;  (2)  the  loss  of  the  external  ears;  (3)  the 
shortening  and  deflection  of  the  basal  joints  of  the  legs; 
(4)  elongation  of  the  rear  portion  of  the  body.  Caudal 
propulsion  is  attained  in  the  whales  by  the  huge 
dorsally  flattened  tail;  in  the  seals  (whose  ancestors 
were  perhaps  tailless)  by  the  backwardly  directed  hind 
legs. 

Compared  with  these  marine  mammals  those  of  our 
fresh  waters  show  very  moderate  departures  from 
terrestrial  form.  The  beaver  has  broadly  webbed  hind 
feet  for  swimming.  The  muskrat  has  a  laterally 
flattened  tail.  The  mink,  the  otter  and  the  fisher,  with 
their  elongate  bodies  and  paddle-like  legs,  are  best 
fitted  for  life  in  the  water,  and  spend  much  time  in  it. 
But  all  fresh-water  mammals  make  nests  and  rear  their 
young  on  land. 

Ill 

The  insects  that  live  in  the  water  have  adaptations  for 
swimming  that  parallel  those  of  mammals,  just  noted; 
but  some  other  adaptations  grow  out  of  the  different 
nature  of  their  respiratory  system,  and,  more  grow  out 
of  the  difference  in  their  life  cycle.  The  free -living 
larval  stage  of  insects  offers  opportunity  for  independ- 
ent adaptation  in  that  stage.  Adult  insects  of  but  two 
orders,  Coleoptera  and  Hemiptera,  are  commonly 
found  in  the  water.  These,  as  compared  with  their 
terrestrial  relatives,  exhibit  many  of  the  same  adapta- 
tions already  noted  in  mammals ;  ( 1 )  approximation  to 
stream-line  form,  with  (2)  consolidation  of  the  forward 
parts  of  the  body  for  greater  rigidity;  (3)  lowering  of 
the  eyes  and  smoothing  of  all  contours;    (4)  loss  of  hair 


274      Adjustment  to  Conditions   of  Aquatic  Life 

and  sculpturing,  and  (5)  shortening  of  basal  segments  of 
swimming  legs,  with  lengthening  of  their  oar-like  tips, 
flattening  and  flexing  of  them  into  the  horizontal  plane, 
and  limiting  their  range  of  motion  to  horizontal  strokes 
in  line  with  the  axis  of  gravity  of  the  body.  Caudal 
propulsion  does  not  occur  with  adult  insects;  none  of 
them  has  a  flexible  tail.  Oar-like  hind  feet  are  the 
organs  of  propulsion.  The  best  swimmers  among  them 
are  a  few  of  the  larger  beetles :  Cy bister,  which  swims 
like  a  frog  with  synchronous  strokes  of  its  powerful 
hind  legs,  and  Hydrophilus,  with  equally  good  swimming 
legs,  which,  like  the  whale,  has  developed  a  keel  for 
keeping  its  body  to  rights. 

Adult  insects,  like  the  mammals,  lack  gills,  and  rise 
to  the  surface  of  the  water  for  air;  but  they  take  the 
air  not  through  single  pairs  of  nostrils,  but  a  number  of 
pairs  of  spiracles,  and  they  receive  it,  not  into  lungs, 
but  into  tracheal  tubes  that  ramify  throughout  the 
body.  The  spiracles  are  located  at  the  sides  of  the 
thorax  and  abdomen,  in  general  a  pair  to  each  seg- 
ment. 

In  diving  beetles  the  more  important  of  these  are 
the  ones  located  on  the  abdomen  beneath  the  wings. 
Access  to  these  is  between  the  wing  tips.  The  beetles 
when  taking  air  hang  at  the  surface  head  dowmward. 
The  horny,  highly  arched,  fore  wings  are  fitted  closely 
to  the  body  to  inclose  a  capacious  air  chamber.  They 
are  opened  a  little  at  their  tips  for  taking  in  a  fresh  air 
supply  at  the  surface.  Then  they  are  closed,  and  the 
beetle,  swimming  down  below,  carries  a  store  of  air  with 
him. 

In  other  beetles  there  are  different  methods  of  gather- 
ing and  carrying  the  air.  The  little  yellow-necked 
beetles  of  the  family  Haliplidae,  gather  the  air  with  the 
fringed  hind  feet,  pass  it  forward  underneath  the  huge 
ventral  plates  wrhich,  in  these  beetles  cover  the  bases 


Aquatic  Adaptations  of  Insects  275 

of  the  hind  legs,  and  thence  it  goes  through  a  transverse 
groove-like  passage  (fig.  168)  to  a  chamber  underneath 
the  wing  bases,  where  there  are  two  enlarged  spiracles 
on  each  side.  The  beetles  of  the  family  Hydrophilidse 
have  their  ventral  surface  covered  with  a  layer  of  fine 
water-repellant  pubescence,  to  which  the  air  readily 
adheres.  Thus  the  air  is  carried  exposed  upon  the 
surface,  where  it  shines  like  a  breastplate  of  silver. 

In  the  waterbugs,  the  air  is  usually  carried  on  the 
back  under  the  wings,  but  the  inverted  back-swimmers 
conduct   air   to   their   spiracles   through   longitudinal 


Fig.  168.  Diagram  of  the  air- taking  apparatus  of  the  beetle, 
Haliplus.  The  arrow  indicates  the  transverse  groove  that 
leads  to  the  air  chamber.     (From  Matheson.) 

grooves  that  are  covered  by  water-repellant  hairs,  and 
that  extend  forward  from  the  tip  of  the  abdomen  upon 
the  ventral  side.  The  water  walking-stick,  Ranatra, 
and  some  of  its  allies  have  developed  a  long  respirat<  >rv 
tube  out  of  a  pair  of  approximated  grooved  caudal 
stylets.  This  long  tail-like  tube  reaches  the  surface 
while  the  bug  stays  down  below,  breathing  like  a  man 
in  a  diving  bell. 

The  immature  stages  of  aquatic  insects  are  far  more 
completely  adapted  to  life  in  the  water  than  arc  the 
adults.     Some  members  of  nearly  all  the  orders,  and  all 


276      Adjustment  to  Conditions  of  Aquatic  Life 


the  members  of  a  few  of  the  smaller  orders  live  and  grow 
up  in  the  water.  These  facts  have  been  noted,  group 
by  group,  in  Chapter  IV.  Here  we  may  explain  that 
the  reason  for  this  probably  lies  in  the  greater  plasticity 
of  the  immature  stages.  All  are  thin-skinned  on  hatch- 
ing from  the  egg,  and  a  supply  of  oxygen  may  be  taken 
from  the  water  by  direct  absorption  thro  the  general 
surface  of  the  body.  With  growth  gills  develop;  but 
these  have  no  relation  to  the  structure  or  life  of  the 
adult  and  are  lost  at  the  final  transformation. 


Fig.  169.  Adult  aquatic  insects:  a,  the 
back  swimmer  (Notonecta) ;  b,  the  water- 
boatman  (Corixa);  c,  a  diving  beetle 
(Dytiscus);   d,  a  giant  water-bug  (Benacus). 

Here  again  we  find  all  degrees  of  adaptation.  The 
larvae  of  the  long-horned  leaf  beetles  (Donacia,  etc.) 
that  live  wholly  submerged  have  solved  the  problem  of 
getting  air  by  attaching  themselves  to  plants  and  per- 
forating the  walls  of  their  internal  air  spaces,  thus 
tapping  an  adequate  and  dependable  air  supply  that  is 
rich  in  oxygen.  This  method  is  followed  also  by  the 
larvae  of  several  flies  and  at  least  one  mosquito.  There 
are  many  aquatic  larvae  that  breathe  air  at  the  surface 
as  do  adult  bugs  and  beetles.  Some  of  these,  such  as 
the  swaleflies  and  craneflies,  (fig.  215)  differ  little  from 
their  terrestrial  relatives.  Others  like  the  mosquito 
are  specialized  for  swimming  and  breathe  thro  respira- 
tory   trumpets.     A    few    like    the    rat-tailed    maggot 


Aquatic  Adaptations  of  Insect  Lan 


rvce 


277 


parallel  the  method  of  Ranatra  mentioned  above  in 
that  they  have  developed  a  long  respiratory  tube, 
capable  of  reaching  the  surface  of  the  water  while  they 
remain  far  below. 


Fig.  170.     Tracheal  gill  of  the  mayfly  nymph,  Heptagenia,  show- 
ing loops  of  tracheoles  toward  the  tip. 


Of  those  that  breathe  the  air  that  is  dissolved  in  the 
water  a  few  lack  gills  even  when  grown  to  full  size;  but 
these  for  the  most  part  live  in  well  aerated  waters,  and 
possess  a  copious  development  of  tracheae  in  the  thinner 
portions  of  their  integument.  Such  are  the  pale 
nymphs  of  the  stonefly,  Chloroperla,  that  live  in  the 


278      Adjustment  to  Conditions  of  Aquatic  Life 

rapids  of  streams  and  the  slender  larvae  of  the  punkie 
Ceratopogon,  that  live  where  algae  abound. 

The  gills  of  insect  larvae  are  of  two  principal  sorts: 
blood-gills  and  tracheal  gills.  Blood-gills  are  cylindric 
outgrowths  of  the  integument  into  which  the  blood 
il<  >ws.  Exchange  of  gases  is  between  the  blood 
inside  the  gills  and  the  water  outside.  Such  gills 
are  most  commonly  appended  to  the  rear  end  of  the 
alimentary  canal,  a  tuft  of  four  retractile  anal  gills 
being  common  to  many  dipterous  larvae.  Bloodworms 
have  also  two  pairs  developed  upon  the  outside  wall  of 
the  penultimate  segment  of  the  body  (see  fig.  236  on 
P-  393)-     Such  gills  are  most  like  those  of  vertebrates. 

Tracheal  gills  are  more  common  among  insect  larvae. 
These  are  similar  outgrowths  of  the  skin,  traversed  by 
fine  tracheal  air-tubes.  In  these  the  exchange  of  gases 
is  between  the  water  and  the  air  contained  within  the 
tubes,  and  distribution  of  it  is  thro  the  complex  system 
of  tracheae  that  ramify  throughout  the  body.  The 
tracheae  where  they  enter  such  a  gill  usually  split  up 
into  long  fine  multitudinous  tracheoles  that  form 
recurrent  loops,  rejoining  the  tracheal  branches  (fig. 
170). 

Tracheal  gills  differ  remarkably  in  form,  position  and 
arrangement.  In  form  they  are  usually  either  slender 
cylindric  filaments,  or  small  flat  plates.  Filamentous 
gills  are  more  common,  only  this  sort  occurring  on  stone- 
fly  nymphs  (fig.  1 1 1  on  p.  204),  and  on  caddis-worms. 
Lamelliformor  plate-like  gills  occur  on  the  back  of  may- 
flies (fig.  113),  and  on  the  tail  of  damselflies  (fig.  115). 
Either  kind  may  grow  singly  or  in  clusters.  Filament- 
ous gills  are  often  branched.  In  the  stonefly,Taeniop- 
teryx,  they  are  unbranched  but  composed  of  three  some- 
what telescopic  segments.  Both  filamentous  and 
lamelliform  gills  occur  on  many  mayflies. 


Aquatic  Adaptations  of  Insect  Lt 


irva 


279 


There  is  another  form  of  tracheal  gills,  sometimes 
called  "tube  gills"  developed  upon  the  thorax  of  many 
dipterous  pupae.  Whatever  their  U  >rm 
they  are  merely  hollow  bare  chitin<  >us 
prolongations  from  the  mouth  of  the 
prothoracic  spiracle.  They  are  ex- 
panded "respiratory  trumpets"  in 
mosquito  pupae,  branching  horns  in 
black-fly  pupae,  and  fine  brushes  of 
silvery  luster  in  bloodworm  pupae. 
No  pupae,  save  those  of  the  caddis- 
flies,  have  tracheal  gills  of  the  ordi- 
nary sort. 

Gills  are  developed  rarely  on  the 
head,  more  often  on  the  thorax,  and 
very  frequently  on  the  abdomen. 
They  grow  about  the  base  of  the  maxil- 
lae in  a  few  stonefly  and  mayfly 
nymphs,  about  the  bases  of  the  legs 
in  most  stonefly  nymphs  and  almost 
anywhere  about  the  sides  or  end  of 
the  abdomen  in  all  the  groups.  They 
are  ventral  in  the  spongilla  flies,  dorsal 
in  the  mayflies,  lateral  in  the  orl-rly 
and  beetle  larvae,  caudal  in  the  damsel- 
flies,  anal  in  most  dipterous  larvae, 
and  they  cover  the  inner  walls  of  a 
rectal  respiratory  chamber  in  dragon- 
flies.  Such  extraordinary  diversity  in 
structures  that  are  so  clearly  adaptive 
is  perhaps  the  strongest  evidence  of 
the  independent  adaptation  of  many 
insect  larvae  to  aquatic  life. 
Propulsion  by  means  of  fringed  swimming  legs 
occurs  in  a  few  insect  larvae,  such  as  the  caddis-worm, 


Fig.  171.  Tube-gills 
of  Dipterous  pupae : 
a,  of  a  mosquito, 
Culex ;  b,  of  a  black- 
fly,  Simulium ;  c, 
of  a  midge,  Chiro- 
nomus.  (a  and  b 
detached). 


Triaenodes,  and  the 


water-tiger 


Dvtiscus. 


The  gill 


280       Adjustment  to  Conditions  of  Aquatic  Life 

plates  of  many  mayflies  and  damselflies  are  provided 
with  muscles,  and  these  are  used  for  swimming. 
Caudal  propulsion  is  also  the  rule  in  these  same  groups. 
Among  beetle  and  fly  larvae  locomotion  is  mainly 
effected  by  wrigglings  of  the  body,  that  are  highly 
individualized  but  only  moderately  efficient,  if  judged 
by  speed. 

It  is  worthy  of  note  that  the  completest  adaptations 
to  conditions  of  aquatic  life  do  not  occur  in  those  groups 
of  insects  that  are  aquatic  in  both  adult  and  larval 
stages.  Beetle  larvae  and  water-bug  nymphs  take  air 
at  the  surface,  and  in  structure  differ  but  little  from 
their  terrestrial  relatives.  Fine  developments  of  tra- 
cheal gills  occur  in  the  nymphs  of  mayflies  and  stone- 
flies,  and  in  caddis  worms;  internal  gill  chambers,  in  the 
dragonfly  nymphs;  attachment  apparatus  for  with- 
standing currents,  in  some  dipterous  larvae;  the  utmost 
adaptability  to  all  sorts  of  freshwater  situations  occurs 
in  the  midges;  and  in  adult  life  these  insects  are  all 
aerial. 

What  then  is  the  explanation  of  the  dominance  of 
this  remarkable  insect  group  in  the  world  to-day — a 
dominance  as  noteworthy  in  all  shoal  freshwaters  as  it 
is  on  land?  What  advantages  has  this  group  over 
other  groups?  There  is  no  single  thing;  but  there  are 
two  things  that,  taken  together,  may  give  the  key  to 
the  explanation.     These  are: 

i.  Metamorphosis,  the  changes  of  form  usually  per- 
mitting an  entire  change  of  habitat  and  of  habits 
between  larval  and  adult  life.  The  breaking  up  of  the 
life  cycle  into  distinct  periods  of  growth  and  reproduc- 
tion permits  development  where  food  abounds. 

2.  The  power  of  flight  in  the  adult  stage  permits  easy 
getting  about  for  finding  scattered  sources  of  food  supply 
and  for  laying  eggs. 


Aquatic  Adaptations  of  Insect  Larva 


281 


In  quickly  growing  animals  no  larger  than  insects 
these  matters  are  very  important;  for  even  a  small  and 
transient  food  supply  may  serve  for  the  nurture  of  a 
brood  of  larvae.  And  if  the  food  supply  be  exhausted 
in  one  place,  or  if  other  conditions  fail  there,  the  adults 
may  fly  elsewhere  to  lay  their  eggs.  The  facts  of 
dominance  would  seem  to  justify  this  explanation,  since 
those  groups  that  most  abound  in  the  world  to-day  are 
in  general  the  ones  in  which  metamorphosis  is  most 
complete  and  in  which  the  power  of  flight  is  best 
developed. 


i 

HHIk^  .                 feiT 

y>   ?;~;«-.4 

7    *  *  ^A 

^-■^^■^P^fft%^^^^rmj^L  * . 

II.     MUTUAL 

ADJUSTMENT 

ARIOUS  phenomena  of 
association  between  non- 
competing  species  are 
manifest  alike  in  terres- 
trial and  aquatic  socie- 
I  ties.  The  occurrence  of 
producers  and  consumers 
is  universal.  Carnivores 
I  eat  herbivores,  and  para- 
I  sites  and  scavengers  fol- 
low both  in  every  natural 
society.  Symbiosis  is  as 
well  illustrated  in  green  hydra  and  green  ciliates  as  in 
the  lichens.  The  mutually  beneficial  association  be- 
tween fungus  and  the  roots  of  green  plants  is  as  well 
seen  in  the  bog  as  in  the  forest.  The  larger  organisms 
evervwhere  give  shelter  to  the  smaller,  and  many  ex- 
amples, such  as  that  of  the  alga,  Nostoc,  that  dwells  in 
the  thallus  of  Azolla,  or  the  rotifer  Notommata  parasita 
that  lives  in  the  hollow  internal  cavity  of  Volvox,  occur 
in  the  water  world . 

We  shall  content  ourselves  here  with  a  very  brief 
account  of  two  associations,  one  of  which  has  to  do 
mainly  with  a  mode  of  getting  a  living,  the  other  with 
providing  for  posterity.  The  first  will  be  insectivoious 
plants;  the  second  the  relations  between  fishes  and 
fresh-water  mussels. 


282 


Insectivorous  Plants 


283 


I 

Insectivorous  plants — The  plants  that  capture  insects 
and  other  animals  for  food  are  a  few  bog  plants  such  as 
sundew  and  pitcher-plant,  and  a  number  of  submerged 
bladderwort  s .  These 
have  turned  tables  on 
the  animal  world.  Liv- 
ing where  nitrogenous 
plant-foods  of  the  or- 
dinary sorts  are  scanty, 
they  have  evolved  ways 
of  availing  themselves 
of  the  rich  stores  of  pro- 
teins found  in  the  bodies 
of  animals.  The  sun- 
dew seems  to  digest  its 
prey  like  a  carnivore; 
the  bladderwort  ab- 
sorbs the  dissolved  sub- 
stance like  a  scavenger. 
Charles  Darwin  studied 
these  plants  fifty  years 
ago,  and  his  account 
('75)  is  still  the  best 
we  have. 

The  sundew,  Dro- 
sera,  captures  insects 
by  means  of  an  adhesive 
secretion  from  the  tips 
of  large  glandular  hairs 

that  cover  the  upper  surface  of  its  leaves  (fig.  [72  . 
The  leaves  are  few  in  number  and  spatulate  in  f<  irm,  and 
are  laid  down  in  a  rosette  about  the  base  of  a  stem, 
flat  upon  the  mud  or  upon  the  bed  of  mosses  in  the 
midst  of  which  Drosera  usually  grows.  They  are  r<  d 
in  color,  and  crowned  and  fringed  with  these  purple 


Fig.  172.  A  leaf  of  sundew  with  a 
captured  caddis-fly.  The  glandular 
hairs  are  bent  downward,  their  tips 
in  contact  with  the  body  of  the 
insect.  Other  erect  hairs  show 
globules  of  secretion  envelopi:  \ 
tips. 


284      Adjustment  to  Conditions  of  Aquatic  Life 

hairs,  each  with  a  pearly  drop  of  secretion  at  its  tip 
sparkling  in  the  light,  like  dew,  they  are  very  attractive 
to  look  upon.  The  insect  that  makes  the  mistake  of 
settling  upon  one  of  these  leaves  is  held  fast  by  the  tips 
of  the  hairs  it  touches:  the  more  it  struggles  the  more 
hairs  it  touches,  and  the  more  firmly  it  is  held.  Ere  it 
ceases  its  struggles  all  the  hairs  within  reach  of  it 
begin  to  bend  over  toward  it  and  to  apply  their  tips  to 
the  surface  of  its  body.  Thus  it  becomes  enveloped 
with  a  host  of  glands,  which  then  pour  out  a  digestive 
secretion  upon  it  to  dissolve  its  tissues.  When  digested 
its  substance  is  absorbed  into  the  tissue  of  the  leaf.  # 

The  pitcher-plant,  Sarracenia,  captures  insects  in  a 
different  way.  Its  leaves  are  aquatic  pitfalls.  They 
rise  usually  from  the  surface  of  the  sphagnum  in  a  bog 
(see  fig.  207  on  p.  350)  on  stout  bases  from  a  deep  seated 
root  stalk.  They  are  veritable  pitchers,  swollen  in  the 
middle,  narrowed  at  the  neck  and  with  flaring  lips. 
The  rains  fill  them.  Insects  fall  into  them  and  are 
unable  to  get  out  again;  for  all  around  the  inner  walls 
in  the  region  of  the  neck  there  grows  a  dense  barrier  of 
long  sharp  spines  with  points  directed  downward. 
This  prevents  climbing  out.  The  insects  are  drowned, 
and  their  decomposed  remains  are  absorbed  by  the 
plant  as  food. 

It  is  mainly  aerial  insects  that  are  destroyed,  flies, 
moths,  beetles,  etc. ;  and  we  should  not  omit  to  note  in 
passing  that  there  are  other  insects,  habituated  to  life 
in  the  water  of  the  pitchers,  and  that  normally  develop 
there.  Such  are  the  larvae  of  the  mosquito,  Aedes 
smithi,  and  of  a  few  flies  and  moths. 

The  bladderworts  (Utricularia)  are  submerged  plants 

that  float  just  beneath  the  surface.     On  their  bright 

green,  finely  dissected  leaves  are  innumerable  minute 

traps  (not  bladders  or  floats  as  the  name  of  the  plant 

'  ^  having  the  appearance  shown  in  the  accom- 


Insectivorous  Plants 


28.S 


panying  figure.     These  capture  small  aquatic  animals, 
such  as  insect  larvas,  crustaceans,  mites,  worms,  etc. 

The  mec- 
hanism of 
the  trap  is 
shown  dia- 
grammati- 
cally  in 
figure  174. 
First  of  all 
there  is  a 
circle  of 
radiat- 
ing hairs 
about  the 
entrance, 
set  diagon- 
ally out- 
ward, like 
the  leaders 
of  a  fisher- 
man's tyke 
net,  and 
well  adapt- 
ed to  turn 
the  free- 
swimming 
water  -  flea 
toward  the 


Fig.  173.  A 
spray  of  the 
c  o  m  m  on 
Madderwort, 
Utricularia. 


proper    point   of    ingress.       Then    there    is    a    trans- 
parent elastic  valve  stopping  the  entrance,  hinged  by 


286       Adjustment  to  Conditions  of  Aquatic  Life 


one  side  so  that  it  will  readily  push  inward,  but  holding 
tightly  against  the  rim  when  pressed  outward.     This 

is  the  most  important 
single  feature  of  the  trap. 
It  makes  possible  getting 
in  easily  and  impossible 
getting  out  at  all.  Dar- 
win speaks  of  a  Daphnia 
which  inserted  an  anten- 
nae into  the  slit,  and  was 
held  fast  during  a  whole 
day,  being  unable  to  with- 
draw it.  On  the  outer 
face  of  the  valve  near  its 
margin  is  a  row  of  gland- 
ular hairs.  These  have 
roundly  swollen  terminal 
secreting  cells.  They  may 
be  alluring  in  function,  tho 
this  has  not  been  proven. 
Directed  backward  across 
the  center  of  the  valve  are 
four  stiff  bristles,  that 
may  be  useful  for  keeping 
out  of  the  passageway  ani- 
mals   too    big    to    pass 


Fig.  174.  Diagram  of  the  mechanism 
of  a  trap  of  one  of  the  common  blad- 
derworts.  A,  The  trap  from  the 
ventral  side,  showing  the  outspread  through  it — SUChaS  might 
leader  hairs  converging  to  the  entrance,  blockade  the  entrance. 
1.  leaders,  r.  rim,  v,  valve.  B,  A 
median  section  of  the  same  r,  rim ;  v, 
valve;  iv,  x,  y,  z,  epidermal  hairs; 
w,  from  the  inner  side  of  the  rim;  x, 
from  the  free  edge  of  the  valve;  y, 
from  the  base  of  the  valve;  z,  from 
the  general  inner  surface  of  the  trap.    decompose(L       New  traps 

are  of  a  bright  translucent  greenish  color;  old  ones  are 
blackish  from  the  animal  remains  they  contain.  The 
inner  surface  of  the  trap  is  almost  completely  covered 


Small  animals  when  en- 
trapped swim  about  for  a 
long  time  inside,  but  in 
the  end  thev  die  and  are 


The  Larva  Habits  of  Fresh-water  Mussels      287 

with  branched  hairs.  These  are  erect  forked  hairs  ad- 
jacent to  the  rim,  and  flat-topped  four-rayed  hairs  over 
the  remainder  of  the  wall  space.  These  hairs  project 
into  the  dissolved  fluids,  as  do  roots  into  the  nutriet 
solutions  in  the  soil,  and  their  function  is  doubtless  the 
absorption  of  food. 

II 
The  larval  habits  of  fresh-water  mussels — The  early  life 
of  our  commonest  fresh-water  mussels  is  filled  with 


Fig.   175.     Small  minnows  bearing  larval 
mussels  (glochidia)  on  their  fins. 

shifts  for  a  living  that  illustrate  in  a  remarkable  way 
the  interdependence  of  organisms.  The  adult  mussels 
burrow  shallowly  through  the  mud,  sand  and  gravel  of 
the  bottom  (as  noted  on  page  108)  or  lie  in  the  shelter  <  & 
stones.  Their  eggs  are  very  numerous,  and  hatch  into 
minute  and  very  helpless  larvae.  For  them  the  vicissi- 
tudes of  life  on  the  bottom  are  very  great.  The  chief 
peril  is  perhaps  that  of  being  buried  alive  and  sn 
ered  in  the  mud.     In  avoidance  of  this  and  as  11 


288      Adjustment  to  Conditions  of  Aquatic  Life 


of  livelihood  during  early  development  the  young 
of  mussels  have  mostly  taken  on  parasitic  habits. 
They  attach  themselves  to  the  fins  and  gills  of  fishes 
(fig.  175)-  There  they 
feed  and  grow  for  a 
season,  and  there  they 
undergo  a  metamor- 
phosis to  the  adult 
form.  Then  they  fall 
to  the  pond  bottom 
and  thereafter  lead 
independent  lives. 

The  eggs  of  the  river-  ^         _^ 

mussels  are  passed  in-  Fig.  176.  A  gravid  mussel  (Symphynota 
+n    tViP    wfltprhihes    of  complanata)  with  left  valve  of  shell  and 

to  tne  watertuoes  01       mantle  removedf  showing  brood  pouch 

the    gills    where     they  (modified  gill)  at  B.     (After  Lefevre  and 

are   incubated    for    a       Curtis-} 

time.  Packed  into  these  passageways  in  enormous 
numbers  they  distend  them  like  cushions,  filling  them 
out  in  various  parts  of  one  or  both  gills  according  to 
the  species,  but  mostly  filling  the  outer  gill.  When 
one  picks  up  a  gravid  mussel  from  the  river  bed  the 
difference  between  the  thin  normal  gill  and  the  gill  that 
is  serving  as  a  brood  chamber  (fig.  176)  is  very  marked. 

Glochidia — In  the  case  of  a  very  few  river  mussels 
{Anodonta  imbecillis,  etc.)  development  to  the  adult 
form  occurs  within  the  brood  chamber;  but  in  most 
river  mussels  the  eggs  develop  there  into  a  larval  form 
that  is  known  as  a  glochidiuni.  This  is  already  a  bivalve 
(fig.  177)  possessing  but  a  single  adductor  muscle  for 
closing  the  valves  and  lacking  the  well  developed  system 
of  nutritive  organs  of  the  adult.  It  is  very  sensitive 
to  contact  on  the  ventral  surface.  In  this  condition 
it  is  cast  forth  from  the  brood  chamber. 


Glochidia  oR< 


If  now  the  soft  filament  of  a  fish's  gill,  or  the  pro- 
jecting ray  of  a  fin  by  any  chance  comes  in  contact  with 
this  sensitive  surface  the  glochidium  will  close  up<  >n  it 
almost  with  a  snap;  and  if  the  fish  be  the  right  kind 
for  the  fostering  of  this  particular  mollusc,  it  will 
remain  attached.  It  is  indeed  interesting  to  see  how 
manifestly  ready  for  this  reaction  are  these  larvae.  If  a 
ripe  brood  chamber  of  Anodonta  (fig.  88  on  p.  180)  be 
emptied  into  a  watch  glass  of  water,  the  glochidia 
scattered  over  the  bottom  will  lie  gaping  widely  and 
will  snap  their  toothed  valves  together  betimes,  whether 
touched  or  not.  And  they  will  tightly  clasp  a  hair 
drawn  across  them. 

Doubtless  gills  become  infected  when  water  contain- 
ing the  glochidia  is  drawn  in  through  the  mouth  and 
passed  out  over  them.  Fins  by  their  lashing  cause 
in  the  water  swirling  currents  that  bring  the  glochidia 
up  against  their  soft  rays  and  thin  edges. 

Glochidia  vary  considerably  in  form  and  size,  in  so 
much  that  with  careful  work  species  of  mussels  can 
usually  be  recognized  by  the  glochidia  alone.  Thus  it 
is  possible  on  finding  them  attached  to  fishes,  to  name 
the  species  by  which  the  fishes  are  infected. 

In  size  glochidia  range  usually  between  .5  and  .05 
millimeter  in  greatest  diameter.  Some  are  more  or 
less  triangular  in  lateral  outline  and  these  have  usually 
a  pair  of  opposed  teeth  at  the  ventral  angle  of  the  valves. 
Others  are  ax-head  shaped  and  have  either  two  teeth  or 
none  at  all  on  the  ventral  angles.  But  the  forms  that 
have  the  ventral  margin  broadly  rounded  and  toothless 
are  more  numerous.  Whether  toothed  or  not  they  are 
able  to  cling  securely  when  attached  in  proper  place  to 
a  proper  host. 

The  part  taken  by  the  fish  in  the  association  is  truly 
remarkable.  The  fish  is  not  a  mere  passive  agent  of 
mussel  distribution.     Its  tissues  repond  to  the  stimulus 


290       Adjustment  to  Conditions  of  Aquatic  Life 


Fig.  177.  Glochidia  and  their  development. 
into  larval  mussels,  a,  b,  c,  d,  stages  in  the 
encystment  of  glochidia  of  the  mussel,  Ano- 
donta,  on  the  fin  of  a  carp;  e  and  /,  young 
mussels  (Lampsilis)  a  week  after  liberation  from 
the  fish;  g,  glochidium  of  the  mussel,  Lampsilis, 
before  attachment.     (After  Le^vre  and   Curtis). 

h,  glochidium  of  the  wash-board  mussel,  Quadrula 
heros,  greatly  enlarged  and  stained  to  show  the 
larval  thread  (I  t)  and  sensory  hair  cells  (s  h  c) 
The   clear   band   is   the   single   adductor   muscle. 

»',  a  gill  filament  of  a  channel  cat-fish  bearing 
an  encysted  glochidium  of  the  warty-back  mussel: 
the  cyst  is  set  off  by  incisions  of  the  filament. 
The  darker  areas  on  the  edges  of  the  valves  indi- 
cate new  growth  of  mussel  shell.     (After  Howard.) 

j.  Encysted  young  of  Plagiola  donaciformis,  showing 

great  growth  of  adult  shell,   beyond  the  margin 

of    glochidial    shell — much    greater    growth    than 

occurs  in  most  species  during  encystment.      (After 

Surber.) 


of  the  glochidia  in  a 
way  that  parallels  the 
response  of  a  plant  to 
the  stimulus  of  a  gall 
insect.  As  a  plant 
develops  a  gall  by  new 
growth  of  tissue  about 
the  attacking  insect, 
and  shuts  it  in  and 
both  shelters  and  feeds 
it,  so  the  fish  develops 
a  cyst  about  the  glo- 
chidium and  protects 
and  feeds  it.  The  tis- 
sues injured  by  the 
valves  of  the  glochi- 
dium produce  new 
cells  by  proliferation. 
They  rise  up  about  the 
larva  and  shut  it  in 
(fig.  177).  They  sup- 
ply food  to  it  until  the 
metamorphosis  is  com- 
plete, and  then,  when 
it  is  a  complete  mussel 
in  form,  equipped  with 
a  foot  for  burrowing 
and  with  a  good  sys- 
tem of  nutritive  or- 
gans, they  break  away 
from  it  and  allow  it 
to  fall  to  the  bottom. 
vSince  this  period  lasts 
for  some  weeks,  or 
even  in  a  few  cases, 
months,  the  fishes  by 


Glochidia  291 

wandering  from  place  to  place  aid  the  distribution  of 
the  mussels,  but  they  do  much  more  than  this. 

It  is  to  be  noted,  furthermore,  that  this  relation  is  a 
close  one  between  particular  species,  just  as  it  is  be- 
tween plants  and  gall  insects.  Each  attacking  species 
has  its  own  particular  host.  Recent  careful  studies 
made  by  Dr.  A.  D.  Howard  and  others  at  the  Fairport 
Biological  Laboratory  have  shown  such  relations  as 
the  following: 

Species  of  Mussels  Host  Species 

1.  Yellow  Sand  Shell  (Lampsilis  anodontoides)  on  the  gars 

2.  Lake  Mucket  (Lampsilis  luteolus)  on  the  basses  and  perches 

3.  Butterfly  Shell  (Plagiola  securis)  on  the  sheepshead 

4.  Warty  Back  (Quadrula  pustulosa)  on  the  channel  catfish 

5.  Nigger-head  (Quadrula  ebeneus)  on  the  blue  herring 

6.  Missouri  Nigger-head  (Obovaria  ellipsis)  on  the  sturgeons 

7.  Salamander  mussel  (Hemilastena  ambigua)  on  Necturus 

Some  of  these  mussels  infect  one  species  of  fish ;  some, 
the  fishes  of  one  family  or  genus ;  a  few  have  a  still  wider 
range  of  host  species,  these  last  being  usually  the 
species  having  the  larger  and  stronger  glochidia  with  the 
best  development  of  clasping  hooks  on  the  valve  tips. 
A  very  special  case  is  that  of  Hemilastena,  a  mussel 
that  lives  under  flat  stones  and  projecting  rock  ledges 
in  the  stream  bed.  Living  in  the  haunts  of  the  mud- 
puppy,  Necturus,  and  out  of  the  way  of  the  fishes,  it 
infects  the  gills  of  this  salamander  with  its  glochidia. 

The  glochidia  will  grow  only  on  their  proper  hosts. 
They  will  take  hold  on  almost  any  fish  that  touches 
them  in  a  manner  to  call  forth  their  snapping  react  i<  >n, 
but  they  will  subsequently  fall  off  from  all  but  their 
proper  hosts,  without  undergoing  development. 

Whether  it  be  the  mussel  that  reacts  only  to  a  certain 
kind  of  fish  substance,  or  the  fish  that  reacts  to  form  a 
cyst  only  for  a  certain  glochidial  stimulus  is  not 
known.  The  relation  appears  onesided,  and  beneficial 
only  to  the  parasitic  mussel;     yet    moderate  infesta- 


292       Adjustment  to  Conditions  of  Aquatic  Life 

tion  appears  to  do  little  harm  to  the  fishes.  The 
cysts  are  soon  grown,  emptied  and  sloughed  off,  leaving 
no  scar.  And  a  few  fishes,  such  as  the  sheepshead 
which  is  host  for  many  mussels,  appear  to  reap  an 
indirect  return,  in  that  their  food  consists  mainly  of 
these  same  mussels  when  well  grown. 

It  may  be  noted  in  passing  that  one  little  European 
fish,  the  bitterling,  has  turned  tables  on  the  mussels. 
It  possesses  a  long  ovipositor  by  means  of  which  it 
inserts  its  own  eggs  into  the  gill  cavity  of  a  mussel, 
where  they  are  incubated. 


$m$% 


CHAPTER   VI 

IC    SOCIETIES 


LIMNETIC 
SOCIETIES 


REAT  bodies  of  water 
furnish  opportunity  for 
all  the  different  lines 
of  adaptation  discus 
in  the  preceding  chap- 
ter. The  sun  shines 
full  upon  them  in  all  its 
life-giving  power.  The 
rivers  carry  into  them 
the  dissolved  food  sub- 
stances from  the  land. 
Wind  and  waves  and 
convection  currents  dis- 
tribute these  substances  throughout  their  waters. 
Both  the  energy  and  the  food  needed  for  the  main- 
tenance of  life  are  everywhere  present.  Here  are 
expanses  of  open  water  for  such  organisms  as  can  float 
or  swim.  Here  are  shores  for  such  as  must  find  shelter 
and  resting  places;  shores  bare  and  rocky;  shores  1<  >w 
and  sandy;  shores  sheltered  and  muddy,  with  bordering 
marshes  and  with  inflowing  streams.  The  character 
of  the  population  in  any  place  is  determined  primarily 
by  the  fitness  of  the  organisms  for  the  conditions  they 
have  to  meet  in  it. 


293 


294  Aquatic  Societies 

For  every  species  the  possible  range  is  determined 
by  climate;  the  possible  habitat,  by  distribution  of 
water  and  land;  the  actual  habitat,  by  the  presence  of 
available  food  and  shelter,  and  by  competitors  and 
enemies. 

Our  classification  of  aquatic  societies  finds  its  basis 
in  physiographic  conditions.  We  recognize  two  princi- 
pal ecological  categories  of  aquatic  organisms: 

I.  Limnetic  Societies,  fitted  for  life  in  the  open  water, 
and  able  to  get  along  in  comparative  independence  of 
the  shores. 

II.  Littoral  Societies,  of  shoreward  and  inland  dis- 
tribution. 

Ifajg     i-^^  ,' Z: - LIMNETIC 


Fig.  178.  Diagram  illustrating  the  distribution  of 
aquatic  societies,  in  a  section  extending  from  an 
upland  marsh  to  deep  water.  The  littoral  region 
is  shaded. 


The  life  of  the  open  water  of  lakes  includes  very  small 
and  very  large  organisms,  with  a  noteworthy  scarcity 
of  forms  of  intermediate  size.  It  is  rather  sharply 
differentiated  into  plancton  and  necton;  into  small  and 
large;  into  free-floating  and  free-swimming  forms. 
These  have  been  mentioned  in  Chapter  V,  where  their 
main  lines  of  adaptation  were  pointed  out.  It  remains 
to  indicate  something  of  the  composition  and  relations 
of  these  ecological  groups. 


Plancton 


295 


I 

PLANCTON 

If  one  draw  a  net  of  fine  silk  bolting-cloth  through 
the  clear  water  of  the  open  lake,  where  no  life  is  visil  Te, 
he  will  soon  find  that  the  net  is  straining  something  out 


Fig.  179.  "Water  bloom"  from  the  surface  of  Cayuga 
Lake.  The  curving  filaments  are  algae  of  the  genus 
Anabaena.  The  stalked  animalcules  attached  to  the 
filaments  are  Vorticellas.  The  irregular  bodies  of 
small  flagellate  cells,  massed  together  in  soft  gelatine, 
are  Uroglenas. 

of  the  water.  If  he  shake  down  the  contents  and  lift 
the  net  from  the  water  he  will  see  covering  its  bottom  a 
film  of  stuff  of  a  pale  yellowish  green  or  grayish  or  bn  >wn- 
ish  color,  having  a  more  or  less  fishy  smell,  and  a 
gelatinous  consistency.  If  he  drop  a  spoonful  of  this 
freshly  gathered  stuff  into  a  glass  of  clear  water  and 


296  Aquatic  Societies 


hold  it  toward  the  light,  he  will  see  it  diffuse  through 
the  water,  imparting  a  dilution  of  its  own  color;  and  in 
the  midst  of  the  flocculence,  he  wTill  see  numbers  of 
minute  animals  swimming  actively  about.  Little  can 
be  seen  in  this  way,  however.  But  if  he  will  examine  a 
drop  of  the  stuff  from  the  net  bottom  under  the  micro- 
scope, almost  a  new  world  of  life  will  then  stand 
revealed. 

It  is  a  world  of  little  things ;  most  of  them  too  small 
to  be  seen  unless  magnified;  most  of  them  so  trans- 
parent that  they  escape  the  unaided  eye.  Here  are  both 
plants  and  animals;  producers  and  consumers;  plants 
with  chlorophyl,  and  plants  that  lack  it;  also,  parasites 
and  scavengers.  And  it  is  all  adrift  in  the  open  waters 
of  the  lake. 

Tho  plancton-organisms  are  so  transparent  and 
individually  so  small,  they  sometimes  accumulate  in 
masses  upon  the  surface  of  the  water  and  thus  become 
conspicuous  as  "water  bloom."  A  number  of  the 
filamentous  blue-green  algae,  such  as  Anabaena,  fig.  179, 
and  a  few  flagellates,  accumulate  on  the  surface  during 
periods  of  calm,  hot  weather.  Anabaena  rises  in  August 
in  Cayuga  Lake,  and  Euglena  rises  in  June  in  the  back- 
waters adjacent  to  the  Lake  (see  fig.  1,  on  page  15). 

The  plants  of  the  plancton  are  mainly  algae.  Bacteria 
and  parasitic  fungi  are  ever  present,  though  of  little 
quantitative  importance.  They  are,  of  course,  import- 
ant to  the  sanitarian.  Of  the  higher  plants  there  are 
none  fitted  for  life  in  the  open  water;  but  such  of  their 
products  as  spores  and  pollen  grains  occur  adventi- 
tiously in  the  plancton.  It  is  the  simply  organized 
algae  that  are  best  able  to  meet  the  conditions  of  open- 
water  life.  These  constitute  the  producing  class. 
These  build  up  living  substance  from  the  raw  materials 
offered  by  the  inorganic  world,  and  on  these  the  life  of 


Planet  on 


297 


all  the  animals  of  both  the  plane  ton  and  the  necton, 
depends. 

These  are  diatoms,  blue-green  and  true-green  algae, 
and  chlorophyl-bearing  flagellates.  Concerning  the 
limnetic  habits  of  the  last  named  group,  we  have  spolo  1: 
briefly  in  Chapter  IV  (pp.  102-108).  Being  equipped 
with  flagella,  they  are  nearly  all  free- swimming. 
Most  important  among  them  are  Ceratium,  Dinobrvon 
and  Peridinium. 

Most  numerous  in  individuals  of  all  the  plancton 
algae,  and  most  constant  in  their  occurrence  throughout 
the  year,  are  the  diatoms  (see  fig.  35  on  p.  1 1 1).  Wher- 
ever and  whenever  we  haul  a  plancton  net  in  the  open 
waters  of  river,  lake  or  pond,  we  are  pretty  sure  to  get 
diatoms  in  the  following  forms  of  aggregation: 

1.  Flat  ribbons  composed  of  the  thin  cells  of  Dia- 
toma,  Fragillaria,  and  Tabelaria. 

2.  Cylindric  filaments  composed  of 
the  drum-shaped  bodies  of  Melosira  and 
Cyclotella. 

3.  Radiating  colonies  of  Asterionella. 

4.  Slender  single  cells  of  Synedra. 
And  we  may  get  less  common  forms 

showing  such  diverse  structures  for  flota- 
tion as  those  of  Stephanodiscus  (fig.  35  1) 
and  Rhizosolenia  (fig.  180);  or  we  may 
get  such  predominantly  shoreward  forms 
as  Navicula  and  Meridion. 

The  blue-green  algae  of  the  plancton 
are  very  numerous  and  diverse,  but  the 
more  common  limnetic  forms  are  these : 

1 .     Filamentous  forms  having : 

(a)  Stiff,  smoothly-contoured  fila- 
ments; Oscillatoria  (see  fig,  34 
on  p.  109)  and  Lyngbya,  etc. 

(b)  Sinuous  nodose  filaments,  Ana- 
baena  (fig.  179),  Aphanizomenon 
etc. 


Fig.   180. 

a,  Rhizosolenia; 

b,  Attheya. 


Aquatic  Societ 


ics 


Fig.  iSi.     Rotifers. 


Plancton  299 


(c)     Tapering  filaments  that  are  immersed  in  m<  »n .• 
or  less  spherical  masses  of  gelatine,  their  points 
radiating  outward;    Gloiotrichia,  Rivularia  I  1  • 
fig.  51,  on  p.  133,  and  52),  etc. 
2.     Non-filamentous  forms  having : 

(a)     Cells  immersed  in  a  mass  of  gelatine,  Micro- 
cystis (including  Polycystis  and  Clathrocystis, 
see  fig.  51  on  p.  133),  Ccelosphaerium,  Chrooco- 
ccus,  etc, 
b)     Cells   arranged    in  a  thin  flat  plate.     Tetra- 
pedia  (fig.  51),  Merismopaedia  (see  fig.  53  on  p. 
135),  etc. 
Representatives  of  all  these  groups,  except  the  one 
last  named,  become  at  times  excessively  abundant  in 
lakes  and  ponds,  and  many  of  them  appear  on  the 
surface  as  "water  bloom." 

Of  the  green  algse  there  are  a  few  not  very  common 
but  very  striking  forms  of  rather  large  size  found  in  the 
plancton.  Such  are  Pediastrum  (see  fig.  44  on  p.  123) 
and  the  desmid,  Staurastum.  There  are  many  minute 
green  algae  of  the  utmost  diversity  in  form  and  arrange- 
ment of  cells.  Most  of  those  that  are  shown  in  figure 
50  on  page  129  occur  in  the  plancton;  Botyrococcus  is 
the  most  conspicuous  of  these.  A  few  filamentous 
green  forms  such  as  Conferva  (see  fig.  45  on  p.  124)  and 
the  Conjugates  (fig.  41  on  p.  1 19),  occur  there  adventi- 
tiously, their  centers  of  development  being  on  shores. 

The  animals  of  the  plancton  are  mainly  protozoans, 
rotifers  and  crustaceans.     The  protozoans  of  the  open 

Fig.  181. 

I,  Philodina.     2, 3,  Rotifer.     4.  Adineta.     5,  Floscularia.      6   Stephanoceros.      7.  A 
8,  Melicerta.     9.  Conochilus.     10,  Ramate  jaws.     11.  Malleo-ramateiaws.     12.  ,M 
codon.     13,  Asol.inchna.      14,  IS,  Synchaeta.      16  Tnarthra.      17.  Hydat.na. 
arthra.      19.  Dlglena.     20,  Durella,      21.  Rattulus.     22,  Dmochans.      23.  24.  Salp^a. 
25,  Euchlanis.      26,   Monostvla.     27.  Colurus.       28,  29.  Pterodina.      30.1B1 
31!  Malleate  jaws.      32,  Xoteus.       33,  34.  Notholca.     35.  ,36.  Anuraea.      37.  I 
38,  Gastropus.     39.  Forcipate  jaws.     40,Anapus.     42,  I-Vu..li<.n. 

From  Genera  of  Plancton  Organisms  of  the  Cayuga  Lake  Ba 
O.  A.  Johannsenand  the  junior  author. 


300 


Aquatic  Societies 


water  are  few.  If  we  leave  aside  the  chlorophyl- 
bearing  flagellates  already  mentioned  (often  considered 
to  be  protozoa)  the  commoner  forms  among  them  are 
such  other  flagellates  as  Mallomonas  (see  fig.  185  on 
page  309),  such  sessile  forms  as  VorticHla  (fig.   179) 


Fig.   182.     Plancton  Cladocerans  from  Cayuga  Lake.     Th,? 
larger,  Acroperus  harper;    the  smaller,  Chydorus  sp. 


and  such  shell-bearing  forms  as  Arcella  and  Diffiugia 
(see  fig.  69  on  p.  159). 

The  rotifers  of  the  plancton  are  many.  The  most 
strictly  limnetic  of  these  are  little  loricate  forms  such 
as  Anuraea  and  Notholca,  two  or  three  species  of  each 
genus.  When  one  looks  at  his  catch  through  a  micro- 
scope nothing  is  commoner  than  to  see  these  little  thin- 


Plancton  -20I 


shelled  animals  tumbling  indecorously  about.  Some- 
times almost  every  female  will  be  carrying  a  single  Large 
egg.  Several  larger  limnetic  rotifers,  such  as  Triarthra, 
Polyarthra  and  Pedalion,  bear  conspicuous  appendages 
by  which  they  may  be  easily  recognized.  The  softer- 
bodied  Synchaeta  will  be  recognized  by  the  pair  of  ear- 
like prominences  at  the  front.  Other  common  limnetic 
forms  are  shown  at  2  (Rotifer  neptunius),  21  and  25  of 
figure  181. 

The  Crustacea  of  fresh-water  plancton  are  its  largest 
organisms.  They  are  its  greatest  consumers  of  vege- 
table products.  They  are  themselves  its  greatest  con- 
tribution to  the  food  of  fishes.  Most  of  them  are 
herbivorous,  a  few  eat  a  mixed  diet  of  algae  and  of  the 
smaller  animals.  The  large  and  powerful  Leptodora  is 
strictly  carnivorous.  The  following  are  the  more 
truly  limnetic  forms : 

I.  Cladocerans;  species  of 

Daphne  (fig.  234)  Diaphanosoma 

Chydorus  Ceriodaphnia  (fig.  165) 

Bosmina  (fig.  9 1 )  Polyphemus 

Sida  Bythotrephes 

Acroperus  (fig.  1S2)  Leptodora.  (fig.  186) 

II.  Copepods;   species  of 

Cyclops  Epischura 

Diaptomus  Limnocalanus 

Canthocamptus  (see  figures  95  and  96) 

Of  plancton  animals  other  than  those  of  the  groups 
above  discussed,  there  are  no  limnetic  forms  of  any 
great  importance.  There  is  one  crustacean  of  the 
Malacostracan  group,  My  sis  relicta,  that  occurs  in  the 
deeper  waters  of  the  great  lakes.  There  is  one  trans- 
parent water-mite,  Atax  crassipes,  with  unusually  Long 


Aquatic  Societies 


and  well  fringed  swimming  legs,  that  may  fairly  be 
counted  limnetic.  There  is  only  one  limnetic  insect. 
It  is  the  larva  of  Corethra — a  very  transparent,  free 
swimming  larva,  having  within  its  body  two  pairs^  of 
air  sacs  that  are  doubtless  regulators  of  its  specific 
gravity. 


Fig.  183.     The  larva  of  the  midge,  Corethra.     (After  Weismann.) 

Seasonal  Range.  There  is  no  period  of  absence  of 
organisms  from  the  open  water,  yet  the  amount  of  life 
produced  there  varies,  as  it  does  on  land,  with  season 
and  temperature.  In  winter  there  are  more  organisms 
in  a  resting  condition,  and  among  those  that  continue 
active,  there  is  little  reproduction  and  much  retardation 
of  development.  Life  runs  more  slowly  in  the  winter. 
Diatoms  are  the  most  abundant  of  the  algae  at  that 
season. 

There  is  least  plancton  in  the  waters  toward  the  end 
of  winter — February  and  early  March  in  our  latitude. 
The  returning  sun  quickens  the  over- wintering  forms, 
according  to  their  habits,  into  renewed  activity,  and 
up  to  the  optimum  degree  of  warmth,  hastens  reproduc- 
tion and  development.  With  the  overturn  of  the 
waters  in  early  spring  comes  a  great  rise  in  the  produc- 
tion of  diatoms,  these  reaching  their  maximum  often- 
times in  April.  This  is  followed  by  a  brisk  develop- 
ment of  diatom-eating  rotifers  and  Crustacea.  Usually 
the  entomostraca  attain  their  maximum  for  the  year  in 
May.  This  rise  is  accompanied  by  a  marked  decline 
in  numbers  of  diatoms  and  other  algae,  due,  doubtless, 
to  consumption  overtaking  production.     The  warmth 


Seasonal  Range  303 


of  summer  brings  on  the  remaining  algae,  first  the  gr<  • 
and  then  the  blue-greens,  in  regular  seasonal  sua 
It  brings  with  them  a  wave  of  the  flagellate  Ceratium, 
which,  being  much  less  eaten  by  animals  than  t 
often  gains  a  great  ascendency,  just  as  the  browsing  of 
grass  in  a  pasture  favors  the  growth  of  the  weeds  that 
are  left  untouched.     Green  algse  reach  their  maximum 
development  in  early  summer,  and  blue-greens,  in  mid 
or  late  summer,  when  the  weather  is  hottest. 

With  the  cooling  of  the  waters  in  autumn,  reproduc- 
tion of  summer  forms  ceases  and  their  numbers  decline. 
The  fall  overturning  and  mixing  of  the  waters  usually 
brings  on  another  wave  of  diatom  production,  followed 
by  the  long  and  gradual  winter  decline.  This  is  < 
accompanied,  as  in  the  spring,  by  abundance  of  Din*  >- 
bryon.  The  flagellate  Synura  (see  fig.  30  on  p.  103 1  is 
rather  unusual  in  that  its  maximum  development  occurs 
often  in  winter  under  the  ice. 

The  coming  and  going  of  the  plancton  organisms 
has  been  compared  to  the  succession  of  flowers  on  a 
woodland  slope ;  but  the  comparison  is  not  a  good  one ; 
for  these  wild  flowers  hold  their  places  by  continuously 
occupying  them  to  the  exclusion  of  newcomers.  The 
planctonts  come  and  go.  They  are  rather  to  be 
likened  to  the  succession  of  crops  of  annual  weeds  in  a 
tilled  field;  crops  that  have  to  re-establish  themselves 
every  season.  They  may  seed  down  the  soil  ere  they 
quit  it,  but  they  may  not  re-occupy  it  without  a  strug- 
gle. And  as  the  weeds  constitute  an  unstable  and 
shifting  population,  subject  to  many  fluctuations,  so 
also  do  the  plancton  organisms.  They  come  and  g<  1 : 
and  while  on  their  going  we  know  that  when  they  c<  >me 
again,  another  season,  they  will  probably  present  c<  »1- 
lectively  a  like  aspect,  yet  the  species  will  be  in  different 
proportions. 


304  Aquatic  Societies 


There  are  probably  many  factors  determining  this 
annual  distribution;  "but  chief  among  them  would  seem 
to  be  these  three: 

1.  Chance  seeding  or  stocking  of  the  waters. 
Each  species  must  be  in  the  waters,  else  it  cannot 
develop  there;  and  for  every  species,  there  are  many 
vicissitudes  (such  as  famine,  suffocation,  and  parasitic 
diseases)  determining  the  seeding  for  the  next  crop. 

2.  Temperature.  Many  plants  and  animals,  as  we 
have  seen,  habitually  leave  the  open  waters  when  they 
grow  cooler  in  the  autumn,  and  reappear  in  them  when 
they  are  sufficiently  warmed  in  the  spring.  They  pro- 
vide in  various  ways  (encystment,  etc.)  for  tiding  over 
the  intervening  period.  Some  of  them  appear  to  be 
attuned  to  definite  range  of  temperature.  Thus  the 
Cladoceran,  Diaphanosoma,  as  reported  by  Birge  for 
Lake  Mendota,  has  its  active  period  when  the  tempera- 
ture is  about  20°  C.  (68°  P.).  For  this  and  for  many 
other  entomostraca  reproduction  is  checked  in  autumn 
by  falling  temperature  while  food  is  yet  abundant. 

3.  Available  Food.  Given  proper  physical  condi- 
tions, the  next  requisite  for  livelihood  is  proper  food. 
For  the  welfare  of  animal  planctonts  it  is  not  enough 
that  algae  be  present  in  the  water;  they  must  be  edible 
algae.  The  water  has  its  weed  species,  as  well  as  its 
good  herbs.  Gloiotrichia  would  appear  to  be  a  weed, 
for  Birge  reports  that  no  crustacean  regularly  eats  it, 
and  it  is  probably  too  large  for  any  of  the  smaller  ani- 
mals. Birge  says  also  ( '96  p.  353) , '  T  have  seen  Daphnias 
persistently  rejecting  Clathrocystis,  while  greedily 
collecting  and  devouring  Aphanizomenon."  Yet 
Strodtmann  C98)  reports  Chydorus  sphccricus  as  feeding 
extensively  on  Clathrocystis,  even  to  such  extent  that 


Plancton  Pulses  305 


its  abundance  in  the  plancton  is  directly  related  to  the 
abundance  of  that  alga.  Each  animal  may  have  its 
food  preference.  The  filaments  of  Lyngbya  are  too 
large  for  the  small  and  immature  crustaceans  to  handle. 
Ceratium  has  too  hard  a  shell;  it  appears  to  be  eaten 
only  by  the  rather  omnivorous  adult  Cyclops.  For 
animal  planctonts  in  general  Anabaena  and  its  allies 
and  the  diatoms  and  small  flagellates  appear  to  be  the 
favorite  food. 

Obviously,  the  amount  of  food  available  to  any 
species  is  in  part  determined  by  the  numbers  of  other 
species  present  and  eating  the  same  things. 

Plancton  pulses — The  organisms  of  the  plancton 
come  in  waves  of  development.  Now  one  and  now 
another  appears  to  be  the  dominant  species.  In  most 
groups  there  are  a  number  of  forms  that  are  competit<  >rs 
for  place  and  food.  The  diatoms  Asterionella, 
Fragillaria  and  Tabelaria  may  fill  the  upper  waters  of 
a  lake  together  or  in  succession.  A  species  of  Diap- 
tomus  may  dominate  the  waters  this  May,  and 
species  of  Cyclops  may  appear  in  its  stead  next  May. 
Yet  while  species  fluctuate,  the  representation  of  the 
groups  to  which  they  belong  remains  fairly  con- 
stant. 

These  sudden  waves  of  plancton  production  are 
made  possible,  as  every  one  knows,  by  the  brief  life 
cycle  of  the  planctonts,  and  by  their  rapid  rate  of 
increase.  If  a  flagellate  cell,  for  example,  divide  no 
oftener  than  every  three  days,  one  cell  may  have  more 
than  a  thousand  descendants,  within  a  month.  The 
rotifer,  Hydatina  is  said  to  have  a  length  of  life  of  some 
thirteen  days,  but  during  most  of  this  time  it  is  rapidly 
producing  eggs,  and  the  female  is  mature  and  ready  to 
begin  egg  laying  in  69  hours  from  hatching.  Some  of 
the  larger  animals  live  much  longer  and  grow  more 


306  Aquatic  Societies 

slowly,  but  even  such  large  forms  as  Daphne  have  an 
extraordinary  rate  of  increase,  as  we  have  already 
indicated  on  pages  1 86  and  187.  The  rises  in  produc- 
tion grow  out  of : 

1.  Proper  conditions  of  temperature,  light,  etc. 

2.  Abundant  food 

3.  Rapid  increase 

Declines  follow  upon  failure  of  any  of  these,  and 
upon  the  attack  of  enemies.  So  swift  are  the  changes 
during  the  growing  season  that  those  who  systematically 
engage  in  the  study  of  a  lake's  population  takeplancton 
samples  at  intervals  of  not  more  than  fourteen  days, 
and  preferably,  at  intervals  of  seven  days. 

Local  Abundance — Plancton  organisms  tend  to  be 
uniformly  distributed  in  a  horizontal  direction.  Al- 
though many  of  them  can  swim,  their  swimming,  as 
we  have  noted  in  the  preceding  chapter,  is  directed  far 
more  toward  maintenance  of  level,  than  toward  change 
of  location.  There  are,  however,  for  many  plancton 
organisms,  well  authenticated  cases  of  irregular  hori- 
zontal distribution,  one  of  which,  for  Carteria,  we 
quoted  on  pages  103  and  104.  Alongside  that  record 
for  a  tittle  flagellate,  let  us  place  Birge's  ('96)  record  for 
the  water-flea,  Daphne  pulicaria,  in  Mendota  Lake. 

'The  Daphnias  occurred  in  patches  of  irregular  extent 
and  shape,  perhaps  10  by  50  meters,  and  these  patches 
extended  in  a  long  belt  parallel  to  the  shore.  The 
surface  waters  were  crowded  by  the  Daphnias,  and 
great  numbers  of  perch  were  feeding  on  them.  The 
swarm  was  watched  for  more  than  an  hour.  The  water 
could  be  seen  disturbed  by  the  perch  along  the  shore 
as  far  as  the  eye  could  reach.  *  *  *  *  On  this 
occasion  the  number  was  shown  to  be  1,170,000  per 
cubic  meter  of  water  in  the  densest  part  of  the  swarm." 


Distribution  in  Depth 


Shoreward  Range— Few  plancton  organisms 
strictly  limited  to  life  in  open  water.  Most  of  them 
occur  also  among  the  shore  vegetation  in  ponds  and 
bays  and  shoals.  They  are  very  small  and  swim  but 
feebly,  and  there  is  room  enough  for  their  activities  in 
any  pool.  They  mostly  belong  in  the  warm  upper 
strata  of  the  lake,  and  similar  conditions  of  environ- 
ment prevail  in  any  pond.  It  is  the  deep  waters  of  the 
lake  that  maintain  uniform  conditions  of  low  and 
stable  temperature,  and  scanty  light;  and  it  is  the 
organisms  of  the  deeper  strata  that  do  not  appear  in  the 
shoals. 

Hence,  though  the  aquatic  seed-plants  pushing  out 
on  a  lake  shore  are  stopped  suddenly  at  given  depth, 
as  with  an  iron  barrier,  the  more  simple  and  primitive 
algae  of  the  plancton  range  freely  into  all  sorts  of  suit- 
able shoreward  haunts.  We  shall  meet  with  them 
there,  commingled  with  numberless  other  forms  that 
have  not  mastered  the  conditions  of  the  open  water. 
In  each  kind  of  situation  (pond,  river  or  marsh  has  each 
its  plancton)  we  shall  find  a  different  assemblage  of 
species.  In  all  of  them  we  shall  find  the  planctonts  are 
less  transparent;  in  none  of  them  will  there  be  quite 
such  uniformity,  from  place  to  place,  as  is  found  in  the 
population  of  the  open  waters  of  the  lake. 

Distribution  in  Depth.  Since  plancton  organisms 
tend  to  be  uniformly  distributed  in  a  horizontal  plane 
one  may  ply  his  nets  at  any  point  on  a  lake  with  the 
expectation  of  obtaining  a  fair  sample;  but  not  so  with 
depth,  except  at  times  when  the  waters  are  in  complete 
circulation.  A  net  drawn  at  the  surface  would  make 
a  very  different  catch  from  one  drawn  at  a  depth  of 
fifty  feet.  Certain  species  found  in  abundance  in  the 
one  would  not  be  represented  in  the  other.  The 
organisms  of  the  lakes  tend  to  be  horizontally  stratifies  1 . 


3o8 


Aquatic  Societies 


Each  species  has  its  own  level ;  its  own  preferred  habi- 
tat, where  it  finds  optimum  conditions  of  pressure,  air, 
temperature  and  light.  Fig.  184  is  a  diagram  of  the 
midsummer  distribution  in  depth  of  seven  important 
synthetic  planctonts  of  Cayuga  Lake. 


I 


11 


Fig.   184.     Diagram   illustrating    midsummer    distribution    of 

seven  important  synthetic  organisms  in  the  first  one  hundred 

feet  of  depth  of  Cayuga  Lake.    &,  Ceratium;  g,  Dinobryon; 

C-Mallomonas;  D,  Anabaena;  ^  Microcystis  (Clathrocystis); 

^JB-  Asterionella;  ^,  Fragillaria. 

(Based  in  part  on  Juday— 15) 

Light  is  the  principal  factor  determining  distribution 
in  depth.  This  we  have  touched  upon  in  Chapter  II, 
under  the  subject  of  " Transparency."  It  is  only  in  the 
upper  strata  of  lakes,  within  the  reach  of  effective  light, 
that  green  plants  can  grow.  Animals  must  likewise 
remain  where  they  can  find  their  food;  whence  it 
results  that  the  bulk  of  the  plancton  in  a  lake  lives  in  its 


Distribution  in   Depth 


.V>«, 


uppermost  part,  the  thickness  of  this  productive 
stratum  varying  directly  with  the  transparency  of  the 
water. 

It  is  not  at  the  surface,  however,  but  usually  a  little 
below  it — a  depth  of  a  meter,  more  or  less — at  which 
the  greatest  mass  of  the  plancton  is  found.  Full  sun- 
light is  perhaps  too  strong;  for  average  planctonts  a 
dilution  of  it  is  preferred.  Free-swimming  planctonts 
such  as  rotifers  and  entomostraca  move 
freely  upward  or  downward  with  char, 
of  intensity  of  light.  Anyone  who  has  seen 
Daphnes  in  a  sunlit  pool  congregating  in 
the  shadow  of  a  water-lily  pad  will  under- 
stand this.  These  animals  rise  nearer  t<  i 
the  surface  when  the  sun  goes  under  a 
cloud,  and  sink  again  when  the  cloud 
passes.  The  extent  of  their  regular  diur- 
nal migrations  appears  to  be  directly  relat- 
ed to  the  transparency  of  the  water. 

Temperature  also  is  an  important  factor 
determining  vertical  distribution.  Forms 
requiring  the  higher  temperatures  are 
summer  planctonts  that  live  at  or  near 
the  surface.  Others  that  are  attuned  to  lower  tem- 
peratures may  find  a  congenial  summer  home  at  a 
greater  depth.  Thus  the  flagellate  Mallomonas  (fig. 
185)  in  Cayuga  Lake  is  rarely  encountered  in  summer 
in  the  uppermost  twenty  feet  of  water,  though  it  is  com- 
mon enough  at  depths  between  30  and  40  feet,  where 
the  temperature  remains  low  and  constant.  The 
average  range  of  Daphne  pulicaria  is  said  to  be  deeper 
than  that  of  other  Daphnias. 

The  gases  of  the  water  have  much  to  do  with  the 
distribution  of  animal  planctonts,  especially  below  the 
thermocline,  where  the  absence  of  oxygen  from  some 
lakes  during  the  summer  stagnation  period  excludes 


Fig.  185.  Mal- 
1  o  m  o  n  a  s 
ploessi. 
(After  Kent.) 


o  Aquatic  Societies 


practically  all  entomostraca.  Certain  hardy  species  of 
Cyclops  and  Chydorus  appear  to  be  least  sensitive  to 
stagnation  conditions.  The  insect  Corethra,  (fig.  183) 
is  remarkable  for  its  ability  to  Rye  in  the  depths,  where 
practically  no  free  oxygen  remains. 

Age  appears  to  be  another  factor  in  vertical  distribu- 
tion. On  the  basis  of  his  studies  of  the  Entomostraca 
of  Lake  Mendota,  Birge  ('96)  has  formulated  for  them 
a  general  law  of  distribution,  to  the  effect  that  (1) 
broods  of  young  appear  first  in  the  upper  waters  of  the 
lake  (quite  near  the  surface) ;  (2)  increase  of  population 
results  in  extension  downward,  and  the  mass  becomes 
most  uniformly  distributed  at  its  maximum  develop- 
ment; (3)  with  decline  of  production  there  is  relative 
increase  of  numbers  in  the  lower  waters. 

Perhaps  this  shifting  downward  merely  corresponds 
to  the  wane  of  vigor  and  progressive  cessation  of  swim- 
ming activities  with  advancing  age. 

In  the  case  of  many  plants  spore  development  or 
eneystment  may  follow  upon  a  seasonal  wave  of  produc- 
tion, with  a  resulting  change  in  vertical  distribution. 
Filamentous  blue-green  algae  develop  spores.  The 
ordinary  vegetative  filaments  are  buoyed  up  in  part  by 
vacuoles  within  the  cells,  that  lessen  their  specific 
gravity;  but  spores  lack  these.  Hence  the  spore-bear- 
ing filaments  settle  slowly  to  the  bottom,  and  may  be 
found  in  numbers  in  the  lower  waters  ere  they  have 
reached  their  winter  resting  place.  Dinobryon  main- 
tains itself  at  the  surface  in  part  by  means  of  the  lash- 
ings of  its  fiagella,  but  when  its  cells  encyst,  the  flagella 
stop,  and  the  fragmenting  colonies  slowly  settle.  Thus, 
both  internal  and  external  conditions  have  much  to  do 
with  vertical  distribution.  In  general  it  may  be  said 
that  during  their  period  of  highest  vegetative  activity 
all  plants  are  necessarily  confined  to  surface  waters; 
that  most  animals  are  closely  associated  with  them, 


Distribution  in  Depth 


on 


but  that  the  constant  fall  of  organic  material  toward 
the  bottom  makes  it  possible  for  some  animals  to  dwell 
in  the  depths,  if  they  can  endure  the  low  temperature 
and  the  other  conditions  found  there.  There  are  s<  >me 
animal  planctonts,  such  as  species  of  Cyclops  and 
Diaptomus,  that  range  the  water  (oxygen  being  pre- 
sent) from  top  to  bottom.  There  are  many  that  are 
confined  during  periods  of  activity  to  the  warmer 
region  above  the  thermocline.  There  are  a  few  like 
Leptodora  that  seem  to  prefer  intermediate  depths, 
and  there  are  a  few 
( Heterocope,  Limno- 
calanus,  Mysis,  etc.) 
that  dwell  in  the  cold 
water  below  the  ther- 
mocline. 

Collectively,  this 
extraordinary  assem- 
blage of  organisms 
that  we  know  as 
plancton  recalls  in 
miniature  the  life  of 
the  fields.  It  has,  in  its  teeming  ranks  of  minute 
chlorophyl-bearing  flagellates,  diatoms  and  other  algae, 
a  quick-growing,  ever-present  food  supply  that,  like 
the  grasses  and  low  herbage  on  the  hills,  is  the  mainstay 
and  dependence  of  its  animal  population.  It  has  in 
some  of  its  larger  algae  the  counterparts  of  the  trees 
that  support  more  special  foragers,  are  less  completely 
devoured,  and  that,  through  death  and  decomposition, 
return  directly  to  the  water  a  much  larger  proportion 
of  their  substance.  It  has  in  its  smaller  herbivorous 
rotifers  and  entomostraca,  the  counterpart  of  the  hordes 
of  rodents  that  infest  the  fields.  It  has  in  its  large, 
plant-eating  Cladocerans,  such  as  Daphne,  the  equiva- 
lent of  the  herds  of  hoofed  animals  of  the  plains;    and 


Fig.  186.     Leptodora. 


Aquatic  Societies 


it  has  at  least  one  great  carnivore,  that,  like  the  tiger, 
ranges  the  fields,  selecting  only  the  larger  beasts  for 
slaughter.  This  is  Leptodora  (fig.  1 86).  It  is  of  phan- 
tom-like transparency,  and  though  large  enough  to  be 
conspicuous,  only  the  pigment  in  its  eye  and  the  color 
of  the  food  it  has  devoured  are  readily  seen.  It  ranges 
the  water  with  slow  flappings  of  its  great,  wing-like 
antennae.  It  can  overtake  and  overpower  such  forms 
as  Cyclops  and  Daphne  and  it  eats  them  by  squeezing 
out  and  sucking  out  the  soft  parts  of  the  body,  rejecting 
the  hard  shell.  Leptodora,  in  a  small  way,  functions 
in  this  society  as  do  the  fishes  of  the  necton. 

The  total  population  of  plancton  in  any  lake  is  very 
considerable.  Kofoid  ('03)  reported  the  maximum 
plancton  production  found  by  himself  in  Flag  Lake  near 
Havana,  111.,  as  667  cubic  centimeters  per  square  meter 
of  surface:  found  by  Ward  ('95)  in  Lake  Michigan, 
176  do.;  found  by  Juday  ('97)  in  the  shoal  water  of 
Turkey  Lake  in  Indiana,  1439  do.  Kofoid  estimated 
the  total  run-off  of  plancton  from  the  Illinois  River  as 
above  67,000  cubic  meters  per  year — this  the  produc- 
tion of  the  river,  over  and  above  what  is  consumed 
by  the  organisms  dwelling  in  it. 

If  we  imagine  the  organisms  of  a  lake  to  be  pro- 
jected downward  in  a  layer  on  the  bottom,  this  thick 
layer  would  probably  represent  a  quantity  of  life  equal 
to  that  produced  by  an  average  equal  area  of  dry  land. 


The  Ned  ok  313 


THE    NECTON 

The  large  free  swimming  animals  of  the  fresh  waters 
are  all  fishes.  Indeed,  as  we  have  already  noted  (p. 
233),  but  a  few  of  the  fishes  range  through  the  open 
waters.  Such  are  the  white-fish,  the  ale-wife  and  the 
ciscos, — all  plancton  feeders, — and  a  few  more 
piratical  species,  like  the  lake  trout  and  the  muskel- 
longes  that  feed  mainly  on  smaller  fishes. 

Necton,  it  will  thus  be  seen,  is  not  a  natural  society. 
It  contains  no  producing  class.  It  is  sustained  by  the 
plancton  and  by  the  products  of  the  shores. 

These  fishes  all  have  a  splendid  development  of 
stream-line  form.  They  all  swim  superbly.  And 
according  as  they  feed  on  plancton  or  on  other  fishes 
they  are  equipped  with  plancton  strainers  or  with 
raptorial  teeth.  Excellent  plancton  strainers  are  those 
of  the  lake  fishes.  They  are  composed  of  the  close-set 
gill-rakers  on  the  front  of  the  gill  arches,  and  they 
strain  the  water  passing  through.  This  mesh  is  adapt- 
ed for  straining  the  larger  animal  planctonts  while  let- 
ting the  lesser  chlorophyl-bearing  forms  slip  thro. 
Thus  the  fishes  reap  the  crop  of  animals  that  is  matur- 
ed, without  destroying  the  sources  for  a  crop  to  come. 


LITTORAL 

SOCIETIES 


NDER  the  sheltering 
influence  of  shores  the 
vascular  plants  may 
grow.  Animals  elude 
the  eyes  of  their  ene- 
mies, not  by  becom- 
ing transparent,  but 
by  taking  on  colors  and  forms  in  resemblance  to  their 
environment.  They  escape  capture,  not  alone  by  fleet- 
ness,  but  also  by  development  of  defensive  armor,  by 
shelter-building  and  by  burrowing. 

Large  and  small  and  all  intermediate  sizes  occur 
together  along  shore,  and  those  that  appear  betimes  in 
open  water  make  shifts  innumerable  for  place  and 
food  and  shelter  for  their  young. 

There  are  many  factors  affecting  the  grouping  of 
littoral  organisms  into  natural  associations,  most  of 
them  as  yet  but  little  studied ;  but  the  most  important 
single  factor  is  doubtless  the  water  itself.  The  density 
of  this  medium  and  the  consequent  momentum  of  its 
masses  when  in  motion  so  profoundly  affect  the  form 
and  habits  of  organisms  that  they  may  be  roughly 
divided  into  two  primary  groups  for  which  are  sug- 
gested the  following  names: 

314 


Lenitic  Societies 


315 


I .  Len itic*  or  still-water  societie s. 

II.  Lotic]  or  rapid-water  societies,  living  in  waves  <  n 
currents. 


LENITIC 

SOCIETIES 


OKED  together,  less  1  >y 
any  common  character 
of  their  own  than  by 
the  lack  of  lotic  charac- 
teristics, we  include 
under  this  group  name 
those  associations  of 
littoral  organisms  that  dwell  in  the  more  quiet  places 
and  show  no  special  adaptations  for  withstanding  the 
wash  of  waves  or  currents.  Wherever  we  draw  the 
line  between  lenitic  and  lotic  regions,  there  will  be 
organisms  to  transgress  it,  for  hydrographic  conditions 
intergrade.  We  have  already  seen  how  many  organ- 
isms transgress  the  boundary  between  limnetic  and 
littoral  regions.  Just  as  in  that  case  we  found  a  fairly 
satisfactory  boundary  where  the  increasing  depth  of  still 
water  is  such  as  to  preclude  the  growth  of  the  higher 
plants,  so  here  the  boundary  between  lenitic  and  lotic 
regions  may  be  placed  where  the  movement  of  the 
water  is  sufficient  to  preclude  the  growth  of  these  same 
plants. 


*Lenis  =  calm,  placid. 
\Lotus  =  washed. 


316  Aquatic  Societies 


The  reason  why  lenitic  societies  include  practically 
the  entire  population  of  vascular  plants  has  already 
been  stated  (p.  145) :  the  plants  have  a  complexity  of 
organization  that  cannot  withstand  the  stress  of 
rapidly  moving  waters.  They  fringe  all  shoals,  how- 
ever, and  they  fill  the  more  sheltered  places  with  growths 
of  extraordinary  density.  In  such  places  they  pro- 
foundly affect  the  conditions  of  life  for  other  organisms : 
the  supplies  of  food  and  light  and  air,  and  the  oppor- 
tunities for  shelter. 

Streams  and  still  waters,  inhabited  by  lenitic  societies, 
may  be  divided  roughly  into  three  categories: 

1.  Those  that  are  permanent. 

2.  Those  that  dry  up  occasionally. 

3.  Those  that  are  only  occasionally  supplied  with 
water. 

These  so  completely  intergrade,  and  so  vary  with 
years  of  abundance  or  scarcity  of  rainfall,  that 
there  is  no  good  means  of  distinguishing  between  them. 
Perhaps  for  the  humid  Eastern  States  and  for  bodies  of 
still  water  the  words  pond  and  pool  and  puddle  convey 
a  sense  of  their  relative  permanence.  The  population 
of  the  pond  is,  like  that  of  the  lake,  to  a  large  extent 
perennially  active.  It  will  be  discussed  in  succeeding 
pages.  That  of  the  pool  is  composed  of  those  forms 
that  are  adjusted  to  drouth:  forms  that  can  forefend 
themselves  against  the  withdrawal  of  the  water  by 
migration,  by  encystment,  by  dessication,  or  by  bur- 
rowing, or  by  sending  roots  down  into  the  moisture  of 
the  bed.  Some  of  these  will  be  mentioned  in  the  dis- 
cussion of  the  population  of  the  marshes.  The  puddles 
have  a  scanty  population  of  forms  that  multiply  rapidly 
and  have  a  brief  life  cycle.  The  synthetic  forms 
among  them  are  mainly  small  flagellates  and  protococ- 


Lenitic  Societies 


31/ 


Fig.  187.    Lick  Brook  near  Ithaca  in  spring.    Its  bed  runs 
dry  later  in  the  season.     (Photo  by  R.  Matheson.) 


3i8 


Aquatic  Societies 


coid  green  algae.  The  herbivores  are  such  short-lived 
crustaceans  as  Chirocephalus  (see  fig.  90  on  p.  184)  and 
Apus,  which  have  long-keeping,  drouth-resisting  eggs; 
such  rotifers  as  Philodina,  remarkable  for  its  capacity  for 
resumption  of  activity  after  dessication ;  such  insects  as 
mosquitoes.  The  carnivores  are  such  adult  water-bugs 
and  beetles  as  may  chance  to  fly  into  them. 

Whether  a  population  shall  be  able  to  maintain  itself 
depends  on  the  continuance  of  favorable  conditions,  at 
least  through  the  period  of  activity  of  its  members. 
In  these  pages  we  shall  give  attention  only  to  the  life 
of  relatively  permanent  waters. 

Plants — The  shoreward  distribution  of  plants  in 
natural  associations  is  determined  mainly  by  two 
hydrographic  factors:  (1)  movement  and  (2)  depth  of 
the  water.  It  is  directly  related  to  exposure  to  waves 
and  to  currents.  Everyone  knows  the  difference  in 
appearance  between  plants  growing  immersed  in  a  quiet 


Fig.  188.  The  forefront  of  the  Canoga  marshes,  where  partly  sheltered 
from  the  waves  of  Cayuga  Lake, clumps  of  the  lake  bulrush  lead  the 
advance  of  the  shore  vegetation. 


Lenitic  Plants  ^iQ 


pool  and  those  growing  on  a  wave-washed  shore.  The 
former  appear  as  if  robed  in  filmy  mantles  of  green,  full- 
fledged  with  leaves,  and  luxuriant.  The  latter  appear 
as  if  stripped  for  action,  unbranched,  slender  and  bare. 
At  one  extreme  are  the  finely-branched  free-floating 
bladderworts  (see  fig.  173  on  p.  285)  at  the  other  are 
such  firmly  rooted,  slender,  naked,  pliant-topped  forms 
as  the  lake  bulrush  (figure  188)  and  eel-grass.  These 
latter  anchor  their  bodies  firmly  and  closely  to  the  s<  >il, 
and  send  up  into  the  moving  waters  overhead  only  s<  >ft 
and  pliant  vegetative  parts,  that  offer  the  least  possible 
resistance  to  the  movement  of  the  water,  and  that,  if 
broken,  are  easily  replaced.  The  long  cylindric  sh<  ><  >ts 
of  the  bulrush  have  their  vessels  lodged  in  the  axis  and 
surrounded  with  a  remarkable  padding  of  air  cushions. 
They  are  not  easily  injured.  The  flat  ribbon-like 
leaves  of  eel-grass  are  marvels  of  adjustability  to  waves. 

Between  these  two  extremes  are  all  gradations  of 
form  and  of  fitness.  Of  the  pool-inhabiting  type  are 
the  water  crow-foot,  the  water  milfoil,  the  water  horn- 
wort;  of  the  opposite  type  are  the  long-leaved  pond- 
weeds  and  the  pipeworts.  Intermediate  are  the  broader- 
leaved  pond  weeds  and  Philotria. 

These  sometimes  are  found  in  running  streams,  but 
they  usually  grow  in  the  beds  in  dense  mutually  sup- 
porting masses  that  deflect  the  current.  If  one  place  a 
current  meter  among  their  tops  he  will  find  little  move- 
ment of  the  water  there. 

There  is  another  place  of  security  from  waves,  f<  >r 
such  plants  as  can  endure  the  conditions  there.  It  is 
on  the  lake's  bed,  below  the  level  of  surface  disturbance. 
The  stoneworts  (see  fig.  55  on  p.  137)  are  branched  and 
brittle  forms,  very  ill  adapted  to  wave  exposure,  and 
most  of  them  live  in  pools,  but  a  few  have  found  this 
place  of  security  beneath  the  waves.  There  are 
extensive  beds  of  Chara  on  the  bottom  of  our  great 


320 


Aquatic  Societies 


kj  Ww-' 


Fig.   189.     Shore-line  vegetation. 


Shore  Plants  -2i 


lakes,  at  a  depth  of  25  feet  more  or  less,  and  within  the 
range  of  effective  light.  Associated  with  these,  but 
usually  on  the  shoreward  side,  are  beds  of  pondweeds. 
Often  there  are  bare  wave-swept  shores  behind  these 
beds  with  no  sign  of  aquatic  vegetation  that  one  can 
see  from  the  shore. 

Depth  of  water  determines  the  adjustment  of  aquatic 
seed  plants  in  three  principal  categories: 

1.  Emergent  aquatics.  These  occupy  the  shallow 
water,  standing  erect  in  it  with  their  tops  in  the  air, 
and  are  most  like  land  plants.  They  are  by  far  the 
most  numerous  in  species. 

2.  Surface  aquatics.  These  grow  in  deeper  water, 
at  the  front  of  (and  oftentimes  commingling  with)  the 
preceding.  The  larger  ones,  such  as  the  water  lilies 
are  rooted  in  the  mud  of  the  bottom,  and  bear  great 
leaves  that  float  upon  the  surface.  The  smaller  ones 
such  as  the  duckweeds  (see  figs.  61  and  62,  p.  149)  are 
free-floating. 

3.  Submerged  aquatics.  These  form  the  outermost 
belt  or  zone  of  herbage.  They  are  most  truly  aquatic 
in  habits.  Except  for  such  forms  as  dwell  in  quiet 
waters,  they  are  rooted  to  the  bottom.  Depth  varies 
considerably  within  this  zone.  It  extends  from  the 
outer  limits  of  the  preceding   (hardly  more  than  five 


Fig.  189. 

A.  Branches  of  four  submerged  water  plants:     (i)  Philolria,  (2)  Cerato- 
phyllum,  (3)  Ranunculus,  (4)  Nais. 

B.  Emergent  aquatics,  including  a  clump  of  arrow  arum;    two  of  the 
pendulous  club-shaped  fruit-clusters  are  seen  at  (5)  dipping  into  the  water. 

C.  Zonal  arrangement  of  the  plants  of  the  shore-line.      The  backgn  mnd 
zone  is  cat-tail  flag  (Typha).     Next  comes  a  zone  of  pickerel- weed  I  i 
deria)  in  full  flower.     Next,  a  zone  of  water  lilies  and  such  other  aquatics 
with  floating  leaves  as  are  shown  in  D  and  E.     In  the  foreground  is  a  zone  of 
submerged  plants — a  mixture  of  such  forms  as  are  shown  in  A  above. 

D.  A  closer  view:     Lemna,  free-floating  and  Marsilia  with  four  parted 
floating  leaves,  and  Ranunculus,  in  tufted  sprays,  submerged. 

E.  The  floating  leaves  and    emergent  flower    spikes  of    a  pondweed, 
Potamogeton.     (Photo  by  L.  S.  Hawkins  ) 


322  Aquatic  Societies 


feet  at  most)  to  the  limits  of  effective  light.  Within 
such  a  range  of  depth  conditions  of  movement,  pressure, 
warmth  and  light  find  also  a  considerable  range;  hence, 
the  forms  differ  at  the  inner  and  outer  margins  of  the 
zone.  Its  forefront  is  usually  formed  by  Chara  as 
stated  above,  and  pondweeds  follow  Chara,  with  a 
number  of  other  forms  usually  commingled,  in  the 
shallower  part. 

These  groups  are  not  free  from  intergradation  since 
some  forms  like  the  spatterdock  (fig.  195  on  p.  335)  are 
in  part  emergent,  and  some  of  the  pondweeds  have  a 
few  floating  leaves.  But  they  are  nevertheless  con- 
venient, and  they  represent  real  ecological  differences. 

Distribution  of  these  plants  in  depth  results  in  their 
zonal  arrangement  about  the  shore  line.  When  all 
are  present  they  are  arranged  in  the  order  indicated. 
It  is  an  inviolable  order ;  for  the  emergent  forms  cut  off 
the  light  from  those  that  cannot  rise  above  the  surface, 
and  the  latter  overshadow  those  that  are  submerged. 
The  zones  may  vary  in  width  and  in  their  component 
species,  but  when  all  are  present  and  crowded  for  room 
they  can  occur  only  in  this  order.  The  two  accompany- 
ing figures  illustrate  zonal  arrangement ;  figure  189C,  on 
a  low  and  marshy  shore;  figure  190,  on  a  more  elevated 
shore,  backed  by  a  terrestrial  flora. 

The  algce  of  littoral  societies  are  those  of  the  plancton 
(practically  all  of  which  drift  into  the  shoals)  plus 
numberless  additional  non-limnetic  forms,  many  of 
which  are  sessile.  As  with  the  vascular  plants,  algas 
that  are  fragile  (see  fig.  198  on  p.  338)  and  the  larger 
that  float  free  (Spirogyra,  etc.)  develop  mainly  in  pools 
and  quiet  waters,  wThile  those  having  great  pliancy  of 
body  (Cladophora,  see  fig.  46  on  p.  125)  and  protective 
covering  (slime-coat  diatoms,  etc.)  are  more  exposed  to 
moving  waters. 


Zfnaljymngement  of  Plants 


show  above  the  ^^pJVZi^- 


3^4 


Aquatic  Societies 


The  animal  population  of  the  shores  is  likewise  dis- 
tributed largely  in  relation  to  water  movement,  or  to 
conditions  resulting  therefrom.  There  is  a  zonal 
arrangement  of  animal  life  along  shores  that  is  only  a 
little  less  definite  than  that  of  plants.  It  is  much  less 
obvious,  for  plants  are  fixed  in  position  and  come  out 
more  into  the  open  and  into  view.  Nevertheless,  even 
the  most  free-roving  animals,  the  fishes,  as  we  have 
already  seen  (p.  233), keep  in  the  main  to  certain  shore- 
ward limits. 

Distribution  in  relation 
to  depth  and  to  character 
of  bottom  comes  out 
clearly  in  Headlee's  stud- 
ies of  the  mussels  of  Win- 
ona Lake.  In  that  lake 
the  play  of  the  waves  on 
shore  yields  a  clean  beach 
line  of  sand  and  gravel, 
and  sifts  the  finer  mater- 
ials into  deeper  water. 
The  succession  is  gravel 
and  sand,  marly  [sand, 
sandy  marl,  coarse  white 
marl,  marly  mud  and  very 
soft  black  mud.  The  last 
named,  beginning  at  a 
depth  of  some  20  feet, 
covers  a  very  large  central  portion  of  the  lake  bottom. 
Mussels  cannot  live  in  it  for  they  sink  too  deeply 
and  the  fine  sediment  clogs  their  gills.  Hence  the 
mussels  are  restricted  to  the  strip  along  shore.  With- 
in this  strip  they  are  arranged  according  to  hard- 
ness of  bottom  and  exposure  to  waves.  The  accom- 
panying diagram  illustrates  the  distribution  of  four  of 
the   common   species.     The   two   Anodontas,    having 


SA/re 

MA8L 

MUO         \ 

0 

10 

20    FT 

3 
>J    t 

J 
j 

2   2 

2   '' 

2    1 

4- 

B 

Fig.  191.  Diagram  of  distribution  of 
mussels  in  Winona   Lake,    Indiana 

A,  outline  of  lake  with  the  mussel  zone 
stippled  and  marked  out  by  two  ten-foot 
contours. 

B,  shews  the  relation  of  four  of  the  common- 
est species  to  depth  and  character  of  bottom: 

1.  Anodonta  edentula.     3.     Unio  rubigniosa. 

2.  Anodonta  grandis.      4.     Lampsilis  Iuteolus. 


Plancton  Animals  32s 


lighter  shells  less  prone  to  sink,  live  in  the  deeper  z<  >n<  - 
of  mixed  marl  and  mud,  and  so  are  able  to  forage  farther 
out  on  the  bottom.  On  account  of  their  thinner  shells 
they  are  excluded  from  residence  near  the  shore  line, 
where  the  waves  would  crush  them.  The  heavier 
shelled  Unio  requires  a  more  solid  bottom  for  its  sup- 
port, and  is  uninjured  by  the  beating  of  heavy  waves. 
Hence,  its  shoreward  distribution.  Lampsilis,  however, 
is  a  more  freely  ranging  form,  having  a  rather  light  shell. 
It  overspreads  the  range  of  all  the  others,  coming  in  the 
less  exposed  places  rather  close  to  shore. 

Plancton  animals — The  animals  of  the  shoreward 
plancton  are  less  transparent  than  those  of  the  lake. 
They  are  also  far  more  numerous.  They  show  more 
color.  The  color  is  often  related  to  situation.  In 
small  ponds  and  marshes  they  are  darker  as  a  rule  than 
in  large  ponds.  They  include  forms  of  very  diverse 
habits  among  which  are  the  following: 

1.  Forms  that  swim  freely  and  continuously  in  the 
more  open  places.  These  only  are  common  to  both 
littoral  and  limnetic  regions. 

2.  Forms  that  are  free  swimming,  but  that  rest 
betimes  on  plants;  Cladocerans  with  adherent  "neck 
organs" ;   Copepods  with  hooked  antennae,  etc. 

3.  Forms  that  can  and  that  do  swim  betimes,  but 
that  more  habitually  creep  on  plants;  many  ostracods, 
copepods  and  rotifers. 

4.  Forms  that  live  on  or  burrow  in  the  slime  that 
covers  stems  or  other  solid  supports,  and  that  swim 
but  poorly  and  but  rarely  in  the  open  water;  Leeches 
and  oligochete  worms,  rhizopods  and  midge  larvae. 

5.  Sessile  forms  that  cannot  swim,  but  that  become 
detached  and  drift  about  passively  in  the  open  water, 
at  certain  seasons;  hydras,  statoblasts  of  fresh-water 
sponges  and  of  bryozoans,  resting  eggs  of  rotifers  and  of 
cladocerans,  etc. 


326  Agnatic  Societies 


Few  of  these  can  thrive  in  the  waters  of  the  limnetic 
region  of  a  lake ;  but  there  is  at  k  ast  one  member  of  the 
first  group  that  takes  advantage  of  an  abundant  supply 
of  food  in  lake  waters,  migrates  out,  and  develops 
enormously,  overshadowing  in  numbers  sometimes  the 
truly  limnetic  forms.  It  is  Chydorus  sphczricus.  It  is 
rather  a  littoral  than  a  limnetic  species,  yet  it  often 
abounds  in  the  open  lakes,  following  a  rich  development 
there  of  blue-green  algae  suitable  for  its  fo<  d. 

SPATIAL  RELATIONS 

A  large  part  of  the  animal  life  of  the  littoral  region  is 
disposed  in  relation  to  upper  and  lower  surfaces  of  the 
water.  This  grouping  by  levels  is  due  to  gravity. 
Where  the  air  rests  upon  the  water,  making  available 
an  unlimited  supply  of  oxygen,  there  at  the  surface  are 
aggregated  forms  that  require  free  air  for  breathing. 
Where  the  water  rests  upon  the  solid  earth,  there  at  the 
bottom  are  the  forms  that  hide  or  burrow  in  the  ground. 

Plants  and  animals  differ  most  markedly  here.  Light 
is  the  prime  requisite  and  source  of  energy  for  chloro- 
phyl-bearing  plants.  It  is  not  light  but  oxygen  that 
holds  many  animals  at  the  surface  of  the  water;  and 
it  is  indifference  to  light  that  allows  many  other  animals 
to  dwell  in  the  obscurity  of  the  bottom. 

Life  on  the  bottom  has  a  number  of  advantages  among 
which  are  the  following : 

1 .  Shelter  is  available. 

2 .  Energy  is  saved  when  a  resting  place  is  found,  and 
continuous  swimming  is  unnecessary. 

3.  Gravity  brings  food  down  from  above. 

4.  Hiding  from  enemies  is  easier  in  absence  of  strong 
light. 

It  has  also  its  perils  chief  among  which  are: 

1.  Failure  of  oxygen    1   either  of  which  may  result 

2.  Excess  of  silt  in  suffocation. 


Spatial  Relations  327 


In  the  last  chapter  we  have  discussed  the  more 
important  lines  of  specialization  that  have  fitted  the 
members  of  the  bottom  population  to  meet  or  to 
profit  by  these  conditions.  Under  the  subject  "pond 
societies,"  further  specific  illustrations  will  be  cited. 

Life  at  the  surface  is  less  tranquil  than  on  the  bott<  an. 
There  are  two  kinds  of  animals  that  can  maintain  them- 
selves there.  (1)  Those  having  bodies  (together  with 
the  air  they  hold  about  them)  lighter  than  the  water; 
which  rise  to  the  surface  like  a  cork  and  have  to  swim 
in  order  to  go  down  below.  These  are  mainly  adult 
insects  whose  problem  of  getting  air  we  have  discussed 
in  the  preceding  chapter. 

(2)  Those  having  bodies  heavier  than  the  water, 
which  maintain  themselves  at  the  surface  by  some  s<  >rt 
of  hold  on  the  surface  film.  If  free-swimming,  they 
have  to  swim  up  to  the  surface  and  break  through  the 
film  before  they  can  use  it  for  support.  Certain  insect 
larvae,  water-fleas,  rotifers,  ciliates,  etc.,  are  of  this 
habit.  Creeping  forms  must  first  climb  up  some 
emergent  stem,  break  through  and  then  glide  away  sus- 
pended underneath  the  film.  Pond-snails  and  hydras 
are  of  this  sort.  In  an  aquarium  one  may  see  either, 
hanging  suspended,  and  dimpling  the  surface  where  the 
foot  is  attached  by  the  downward  pull  on  the  film. 

The  relations  of  certain  water-fleas  to  the  surface  film 
are  particularly  interesting.  For  many  of  these,  such 
for  example  as  Bosmina,  this  is  a  constant  source  of 
peril.  If  in  swimming  a  Bosmina  accidentally  breaks 
through  this  film  it  falls  over  on  its  side  and  is  held  there 
helpless  lying  on  the  surface  unable  to  swim  away. 
Unless  some  disturbance  dash  it  again  beneath  the 
water,  its  only  chance  for  release  seems  to  lie  in 
moulting  its  skin  and  slipping  out  of  it  into  the 
water.     Usually  when  a  catch  of  surface  planet <  -n  fr<  >m 


328  Aquatic  Societies 


Cayuga  is  placed  in  a  beaker,  the  Bosminas  begin 
to  break  through  one  by  one,  and  soon  are  gathered  in  a 
little  floating  company  in  the  center. 

Scapholeberis  (fig.  192),  however,  appears  to  be 
especially  fitted  to  take  advantage  of  the  surface  film. 
It  is  able  to  maintain  a  proper  position  at  the  surface : 
it  possesses  specialized  bristles  for  breaking  the  film  and 
laying  hold  upon  it;  its  ventral  (uppermost)  margin 
is  straightened  and  extended  posteriorly  in  a  long 
spine;  as  much  contact  may  be  had  as  is  needed. 
Suspended  beneath  the  surface,  where  algae  from  below 
and   pollen    from    the   air  accumulate,   Scapholeberis 


Fig.  192.  Scapholeberis  mucronata, 
suspended  beneath  the  surface  film. 
(After  Scourfield.) 

rows  placidly  about,  foraging ;  or  it  is  borne  along  by  the 
towing  of  air  currents  acting  on  the  surface  water — a 
sort  of  submarine  sailing. 

Scapholeberis  is  unique  among  water-fleas  in  this 
habit.  There  is  also  an  Ostracod,  Notodromas,  of 
similar  habit ;  and  it  is  worthy  of  note  that  both  these 
creatures  have  blackish  markings  on  the  ventral  edges 
of  the  valves  and  are  pale  dorsally.  As  in  the  sloths 
which  climb  inverted  in  trees,  the  usual  coloration  of  the 
body  is  reversed  with  reversal  of  position. 

Then  there  are  some  little  creatures  that  take  advan- 
tage of  the  tenacity  of  the  surface  film  to  cover  them- 
selves with  it  as  with  a  veil.  Copepods,  ostracods, 
rotifers  and  what  not,  climb  up  the  surface  of  emergent 
stems,  pushing  a  film  of  water  ahead  until  they  are  well 
above  the  general  surface  level,  where  they  rest  and 


Spatial  Relations 


feed,  and  find  more  oxygen.  The  larva  of  Dixa  is  one 
of  the  most  interesting  of  these.  It  will  float  in  the 
surface  film,  but  not  for  long,  if  any  support  be  at  hand. 
Touching  a  leaf  it  immediately  bends  double,  and 
pushes  forward  by  alternate  thrusts  at  both  ends,  until 
it  has  lifted  a  film  of  water  to  a  satisfactory  level. 

On  the  surface  are  deposited  the  eggs  of  many  insects 
having  aquatic  larvae,  but  these  eggs  are  heavier  than 

water,  and  unless  anchored  to  i 
some  solid  support  or  buoyed 
up  with  floats  (as  are  such  eggs 
as  those  of  Culex  and  Core- 
thra)  nearly  all  of  them  settle 
to  the  bottom.  There  are, 
however,  a  few  midges  whose 
egg-clusters  float  freely.  A 
brief  account  of  the  egg-lay- 
ing of  one  of  them,  Chironomus 
meridionalis,  will  illustrate 
several  points  of  dependence 
on  the  surface  tension. 

The  female  midge,  when 
ready  to  lay  her  eggs,  rests 
for  a  time  on  some  vertical 
stem  by  the  water  side  in  the 
attitude  illustrated  in  figure 
194.  She  extrudes  her  eggs 
which  hang  suspended  at  the 
She  then  flies  over  the  water 
carrying  them  securely  in  a  rounded  clump  of  gelatin. 
After  a  long  preparatory  flight,  consisting  of  coursing 
back  and  forth  in  nearly  horizontal  lines  at  shoul- 
der height  above  the  surface  of  the  water — a  per- 
formance that  lasts  often  twenty  minutes — she 
settles  down  on  the  surface  and  rests  there  with 
outspread  feet.     The  usefulness  of  her  elongate  tarsi  is 


Fig.  193.  Larva  of  a  Dixa 
midge,  inverted,  to  show:  a, 
caudal  lobe;  b,  creeping 
bristles;  c,  prolegs.  The 
arrow  indicates  the  direction 
of  locomotion,  middle  fore- 
most, both  ends  trailing. 

tip  of  the  abdomen. 


330 


Aquatic  Societies 


here  apparent.  They  rest  like  long  out-riggers  radiately 
arranged  upon  the  surface,  easily  supporting  her  weight 
while  she  liberates  the  egg  mass  and  lets  it  down  into 
the  water.  At  the  top  of  the  egg  clump  appears  a  cir- 
cular transparent  disc  from  which  the  egg  mass  depends. 
This  disc  catches  upon  the  surface  film,  tho  pulled 
down  into  it  in  a  little  rounded  pit-like  depression 
by  the  weight  of  the  eggs.  Slowly 
the  eggs  descend  pulling  out  the  gelatin 
attaching  them  to  the  disc  into  a  slender 
thread  that  thus  becomes  stretched  to 
a  length  of  several  inches.  The  female 
flies  away  to  the  shore  and  leaves  them 
so.  Then  they  drift  about  like  floating 
mines,  transported  by  breezes  and  cur- 
rents. This  little  disc  of  gelatin  dimp- 
ling the  surface  film  is  indeed  a  frail 


rlG.    194. 


The  cg^-laving  of  Chironomus  mcridionnlis. 


A ,  The  female  at  rest  extruding  the  egg-mass.  _ 

B   Tne  female  resting  on  the  surface  film,  letting  the  egg  mass  down  into  the  water. 
C  and  D,  The  egg  mass  liberated  and  hanging  suspended  from  the  surface  film  by  a  delicate 
gelatinous  curd  attached  to  a  small  disc-like  float. 

bark  for  their  transportation.  When  driven  by  waves 
and  currents,  they  break  their  slender  moorings  and 
settle  to  the  bottom,  or  adhere  to  floating  stems 
against  which  they  are  tossed. 

There  is  another  phenomenon  of  the  water  surface  so 
curious  and  interesting  it  merits  passing  mention  here. 
There  is  a  black  wasp  Priocnemis  fiavicornis,  occasion- 
ally seen  on  Fall  Creek  at  the  Cornell  Biological  Field 


Spatial  Relations  *  1 1 

Station,  that  combines  flying  with  water  trans]  m  >rtati<  >n. 
Beavers  swim  with  boughs  for  their  dam,  and  water- 
striders  ran  across  the  surface  carrying  their  1  m  n  >ty,  1  >ut 
here  is  a  wasp  that  flies  above  the  surface  towing  a  l<  >ad 
too  heavy  to  be  carried.  The  freight  is  the  body  « 
huge  black  spider  several  times  as  large  as  the  body  of 
the  wasp.  It  is  captured  by  the  wasp  in  a  waterside 
hunting  expedition,  paralyzed  by  a  sting  adroitly 
placed,  and  is  to  be  used  for  provisioning  her  n< 
It  could  scarcely  be  dragged  across  the  ground,  cl<  >thed 
as  that  is  with  the  dense  vegetation  of  the  water- 
side; but  the  placid  stream  is  an  open  highway.  (  Kit 
onto  the  surface  the  wasp  drags  the  huge  limp  black 
carcass  of  the  spider  and,  mounting  into  the  air  with  her 
engines  going  and  her  wings  steadily  buzzing,  she  sails 
away  across  the  water,  trailing  the  spider  and  leaving 
awake  that  is  a  miniature  of  that  of  a  passing  steamer. 
She  sails  a  direct  and  unerring  course  to  the  vicinity  <  >f 
her  burrow  in  the  bank  and  brings  her  cargo  ashore 
at  some  nearby  landing.  She  hauls  it  upon  the  bank 
and  then  runs  to  her  hole  to  see  that  all  is  ready. 
Then  she  drags  the  spider  up  the  bank  and  into  her 
burrow,  having  saved  much  time  and  energy  by  making 
use  of  the  open  waterway. 

Intermediate  between  surface   and  bottom  the  lif< 
the  water  that  is  not  included  in  either  of  the  two  sir:  it  a 
we  have  just  been  discussing,  but  that  has  continuous 
free  range  of  the  open  water,  is  still  considerable.      It 
corresponds  in  part  to  the  plancton  of  the  open  waft 
as  we  have  seen.     It  corresponds  in  part,  also,  to  the 
necton;  and,  as  in  the  open  water,  so  also  in  the  shoals, 
the  larger  and  more  important  free- swin lining  ai    i 
are  fishes.     Its  spatial  relations  are  complicated  1  »y  the 
habit    some    air-breathing    forms    (especially    in. 
have   of  ranging   downward  freely  thro  the   depths; 


332  Aquatic  Societies 


also  by  the  way  in  which  forms  like  Chironomus,  that 
ordinarily  remain  in  hiding  in  the  bottom,  come  out 
betimes  in  the  open  and  take  a  swim.  But  there  yet 
remain  at  least  two  classes  of  organisms  that  belong 
neither  to  the  top  nor  to  the  bottom,  nor  yet  to  the 
free-swimming  population.  These  are  forms  that  are 
able  to  sustain  themselves  above  the  mud  by  taking 
advantage  of  plant  stems  or  other  solid  supports.  These 
get  their  oxygen  from  the  water.     They  are: 

1.  Climbing  forms,  that  hold  on  by  means  of  claws, 
as  do  the  scuds  and  some  dragonfly,  damselfly  and  may- 
fly larvae,  or  by  a  broad  adhesive  foot  as  do  certain 
minute  mussels.  Many  members  of  this  group  find 
temporary  shelter  between  the  leaves  and  scales  of 
plants. 

2.  Sessile  forms  that  remain  more  or  less  per- 
manently attached,  like  sponges,  bryozoans,  hydras, 
etc. 

Many  members  of  both  these  groups  construct  for 
themselves  shelters.  Chironomus,  for  example,  while 
usually  living  in  such  tubes  as  are  shown  in  figure  134 
on  page  226,  is  able  to  creep  about  freely  upon  the 
stem.  Cothurnia  (fig.  73)  and  Stentor,  and  many 
sessile  rotifers  build  themselves  shelters. 

Such  support  may  be  found  on  the  bottom  itself 
where  that  is  hard ;  but  the  bottom  is  soft  where  most 
seed-plants  grow.  Furthermore,  to  ascend  and  remain 
above  the  level  of  the  hordes  of  voracious  bottom 
dwellers  must  be  a  means  of  safety.  It  is  clear,  there- 
fore, that  plants  rising  from  the  bottom  and  branching 
extensively  must  add  enormously  to  the  biological  rich- 
ness of  the  shoals,  by  the  support  and  shelter  they 
afford  to  such  animals  as  these. 

Size — As  on  land  a  weed  patch  is  a  miniature  jungle, 
having  a  population  of  little  insects  roughly  correspond- 


Life  in  Some  Typical  Lenitic  Situations        33v 


ing  in  social  functions  to  the  larger  beasts  of  the  forest, 
so  in  the  water  there  are  large  and  small,  assembled  in 
parallel  associations.  The  larger,  as  a  rule,  inhabit  the 
more  open  places.  Paddle-fish  and  sturgeons  and  gars 
belong  to  the  rivers;  the  quantative  demands  of  their 
appetites  exclude  them  from  living  in  the  brooks  Then 
is  not  a  living  there  for  them.  Little  fishes  belong  to 
the  brooks  and  to  the  shoals.  In  our  diagram  on  page 
233  we  have  already  shown  how  in  a  small  lake  shore- 
ward distribution  of  the  fishes  corresponds  roughly  with 
their  size,  the  largest  ranging  farthest  out,  and  the 
smallest  sticking  most  closely  to  shelter.  The  senior 
author  has  shown  (07)  a  parallel  to  this  in  the  distribu- 
tion of  diving  beetles  in  an  angle  of  the  shore  of  a  weedy 
pond.  Here  the  most  venturesome  beetle  was  Dytiscus 
(see  fig.  129  on  p.  221).  It  was  taken  at  the  front  of 
the  cat-tails  in  about  three  feet  of  water.  The  associa- 
ted species  were  disposed  closely,  tho  not  strictly  in 
accordance  with  their  size,  between  that  outer  fringe 
and  the  shore,  Acilius,  Coptotomus,  Laccophillus, 
Hydroporus,  (see  fig.  130)  Ccelambus  and  Bidessus 
following  in  succession,  the  last  named  (a  mere  molecule 
of  a  beetle,  having  but  yw  the  weight  of  Dytiscus) 
being  found  only  among  the  trash  at  the  very  shore  line. 

LIFE    IX    SOME    TYPICAL    LENITIC    SITUATIONS 

The  association  of  organisms  in  natural  societies  is 
controlled  by  conditions;  but  conditions  intergrade. 
Lakes,  ponds,  rivers,  marshes  all  merge  insensibly, 
each  into  any  of  the  others;  and  their  inhabitants 
commingle  on  their  boundaries.  Yet  thesenames  stand 
for  certain  general  average  conditions  that  we  meet 
and  recognize,  and  with  which  certain  organisms  are 
regularly  associated.  It  will  be  worth  while  for  us  to 
note  the  main  characteristics  of  the  life  of  several  of  the 
more  typical  of  such  situations. 


334 


Aquatic  Societies 


P o)id  societies — The  kind  of  associations  we  now  come 
to  discuss  are  typically  represented  in  ponds,  but  they 
occur  also  in  any  bodies  of  standing  fresh  water,  that 
are  not  too  deep  for  growth  of  bottom  herbage,  nor  too 
exposed  to  wind  and  wave  for  the  growth  of  emergent 


Fig.  195.  Where  marsh  and  pond  meet.  The  head  of  "the  cove"  at  the  Cor- 
nell Biological  Field  Station.  Beds  of  spatterdock  backed  by  acres  of  cat- 
tail flag.     Neguena  valley  in  the  distance. 

aquatics  along  shore.  The  same  forms  will  be  found 
in  ponds,  lagoons,  bayous,  sheltered  bays  and  basin- 
like expansions  of  streams.  The  bordering  aquatics 
will  tend  to  be  arranged  in  zones,  as  discussed  in  the 
preceding  pages,  according  to  the  closeness  of  their 
crowding. 

1.     The  shoreward  zone  of  emergent  aquatics  will 
include,  in  our  latitude,  species  of  cat-tail  (Typha),  of 


Pond  Societies 


bur-reed  (Sparganium) ,  of  bulrush  (Scirpus),  of  spi 
rush  (Eleocharis),  of  water  plantain  (Alisma),  of  am  >w- 
head  (Sagittaria) ,  and  arrow-arum  (Peltandra),  of] 
erel-weed  (Pontederia) ,  of  manna  grass  (Glyceria),  - 

2.  The  intermediate  zone  of  surface  aquatics  will 
include  such  as: 

(a).  These  rooted  aquatics  with  floating  leaves: 
white  water-lily  (Castalia),  spatterdock  (Nymphaea), 
water  shield  (Brasenia),  pondweed  (Potomogeton),  etc. 


"h 

■ 

\  V 

ytKyj 

¥>kz4$ 

»m,.  Air- 

N^A  [ft 

ytafH  J 

^ 

%  IK 

£       w         Y   1           S 

w     y*  v     i/\J      * 

,.^_  \  /      ;/ 

/ 

Fic.  196.     A  spray  of  the  sago  pondweed,  Potimogeton,  coated  with 
slime-coat  diatoms,  its  leaf  tips  hearing  dwelling  tubes  ol 
larvae  (Chironomus). 


336  Aquatic  Societies 


(b).  These  free-floating  aquatics;  species  of  duck- 
weed (Lemna,  Spirodela),  water  fernworts  (Azolla, 
Salvinia),  liverworts  (Riccia),  etc. 

3.  An  outer  zone  of  submerged  plants  will  include 
such  forms  as  pondweeds  (Potamogeton),  hornwort 
(Ceratophyllum),  crow-foot  (Ranunculus),  naiad 
(Najas),  eel-grass  (Zostera),  stonewort  (Chara),  etc. 

These  grow  lustily  and  produce  great  quantities  of 
aquatic  stuff  which  serves  in  part  while  living,  but  prob- 
ably in  a  larger  part  wrhen  dead,  for  food  of  the  animal 
population,  and  the  ultimate  residue  of  which  slowly 
fills  up  the  pond.  These  plants  contribute  largely  to 
the  richness  and  variety  of  the  life  in  the  pond,  by 
offering  solid  support  to  hosts  of  sessile  organisms,  both 
plants  and  animals.  Their  stems  are  generally  quite 
encased  with  sessile  and  slime-coat  algae,  rotifers, 
bryozoans,  sponges,  egg  masses  of  snails  and  insects 
and  dwelling  tubes  of  midges  (fig.  196).  Especially  do 
floating  leaves  seem  to  attract  a  great  many  insects  to 
lay  their  eggs  on  the  under  surface.  This  is  doubtless 
a  shaded  and  cleanly  place,  so  elevated  as  to  be  favor- 
able for  the  distribution  of  the  young  on  hatching. 

The  algce  of  ponds  are  various  beyond  all  enumerating. 
It  is  they,  rather  than  the  more  conspicuous  seed-plants, 
that  furnish  the  basic  supply  of  fresh  food  for  the  animal 
population.  Small  as  they  are  individually,  their  rapid 
rate  of  increase  permits  mass  accumulation  which 
often  become  evident  enough.     Such  are: 

( 1 ) .  The  masses  of  filamentous  algae,  (Spirogyra  and 
its  allies;  Ulothrix,  Conferva,  etc.)  collectively  called 
"blanket  algae"  that  lie  half-floating  in  the  water,  or  are 
buoyed  to  the  surface  by  accumulated  oxygen  bubbles. 

(2).  The  beautiful  fringes  of  branching  sessile  algae 
(Chaetophora,  fig.  198,  Cladophora,  etc.)  that  envelop 
every  submerged  stem  as  with  a  drapery  of  green. 


Pond  Animals 


337 


(3).     The  lumps  of  brownish  gelatin  inclosing  com- 
pound colonies  (Rivularia,  see  fig.  52  on  p.  134,  e1 
that  are  likely  to  cover  the  same  stems  later  in  the 
season,  and  that  sometimes  seem  to  smother  the  green 
vegetation. 

(4).     The  spherical  lumps  of  greenish  gelatin  that  lie 
sprinkled  about  over  the  bottom — rather  hard  lumps 
inclosing  compact  masses  of  fila- 
ments of  Nostoc,  etc. 

(5).  The  accumulated  free- 
swimming  forms  that  are  not 
seen  as  discrete  masses,  but  that 
tint  the  wrater.  Volvox  tints  it 
a  bright  green;  Dinobryon,  yel- 
lowish; Trachelomonas,  brown- 
ish;   Ceratium,  grayish,  etc. 

Such  differences  as  these  in 
superficial  aspect,  coming,  as 
many  of  them  do,  with  the  regu- 
larity of  the  seasons,  suggest  to 
one  who  has  studied  them  the 
principal  component  of  the 
masses ;  but  one  must  see  them 
with  the  microscope  for  certain 
determination. 

The  animals  of  the  pond  that  breathe  free  air  are  a  few 
amphibians    (frogs    and    salamanders),    a    few    snails 
(pulmonates)  and  many  insects.     The  insects  fall  into 
four  categories  according  to  their  more  habitual  j 
tions  while  taking  air: 

(1).  Those  that  run  or  jump  upon  the  surface. 
Here  belong  the  water- st riders  and  their  allies — long 
legged  insects  equipped  with  fringed  and  water-repel- 
lent feet  that  take  hold  on  the  surface  film,  but  do  n<  >t 
break  through  it.  Here  belong  many  little  Diptera  that 
rest  down  upon  the  surface  between  periods  of  flying. 


Fig.  197.  Diagram  of  a  lily- 
pad,  inverted,  showing 
characteristic  location  and 
arrangement  of  some 
attached  egg  clusters. 

a,  Physa;    b,    Planorbis;     c,  Trise- 
nodes;     d,  Donacia;     c, 
campa;    /,  Enalla&ma 
into  punctures);     g,   Ni 
(laid  singly) ;    h,  Gyrinus. 


333 


Aquatic  Societies 


g-tails  that  gather 


Here  belong  the  hosts  of  minute  sprin 
in  the  edges  in  sheltered  places,  often  in  such  numbers 
as  to  blacken  the  surface  as  with  deposits  of  soot. 
Minute  as  these  are  they  are  readily  recognized  by 
their  habits  of  making  relatively  enormous  leaps  from 
place  to  place. 

(2).     Those  that  lie  prone  upon  the  surface.     Best 
known  of  these  because  every  where  conspicuous  on  still 


Fig.  198.     Two  fallen  stems  enveloped  with  a  rich  growth 
of  the  alga,  Chcetophora  incrassata. 

waters,  are  the  whirl-i-gig  beetles.  Less  common  and 
much  less  conspicuous  are  the  pupae  of  the  soldier-flies 
(Stratiomyia,  etc.)  and  the  larvae  of  the  Dixa  midges. 

(3).  Those  that  hang  as  if  suspended  at  the  surface, 
with  only  that  part  of  the  body  that  has  to  do  with 
intake  of  air  breaking  through  the  surface  film.  Here 
belong  by  far  the  larger  number  of  aquatic  insects. 
Here  are  the  bugs  and  the  adult  beetles,  alertly  poised, 


Pond  Animals 


339 


with  oar-like  hind  legs  swung  forward,  ready,  so  that  a 
stroke  will  carry  them  down  below  in  case  of  appr< 
of  danger.  Here  hang  the  wrigglers — larvas  and  pupae 
of  mosquitoes.  Here  belong  the  more  passive  larvae  of 
many  beetles  and  flies  and  the  pupae  of  swale-flies  and 
certain  crane-flies. 

(4).     Those  that  rest  down  below,  equipped  with  a 
long  respiratory  tube  for  reaching  up  to  the  surface  f<  >r 


Fig.  199.  Diagram  of  distribution  of  pond  life.  The  right  side 
illustrates  the  zonal  distribution  of  the  higher  plants.  1,  shore 
zone;  2,  standing  emergent  aquatics;  j?f  aquatics  with  floating 
leaves;  4,  submerged  aquatics;  5,  floating  aquatics;  6,  free  swim- 
ming algae  of  the  open  water. 

The  left  side  represents  the  principal  features  of  the  distribution  of 
animals,  r,  s,  t,  u,  forms  that  breathe  air;  v,  w,  x,  y,  and  z,  forms 
that  get  their  oxygen  from  the  water. 

(From  the  Senior  Author's  General  Biology) 

air.     Such  are  Ranatra,  and  the  rat-tailed  maggots  of 
syrphus-flies. 

The  animals  of  the  pond  that  are  more  strictly  aquatic 
in  respiratory  habits  (being  able  to  take  their  oxygen 
supply  from  the  water  itself)  are  so  numerous  that  we 
shall  be  able  to  mention  only  a  few  of  the  larger  and 
more  characteristic  forms.  First  there  are  the  inhabi- 
tants of  the  bottom.  These  fall  into  two  principal  cate- 
gories, the  free-living  and  the  shelter-building  forms. 
The   free-living   forms   may   be   grouped   as   follows: 


340 


Aquatic  Societies 


(i).  Bottom  sprawlers  that  lie  exposed,  or  only 
covered  over  with  adherent  silt.  These  are  character- 
ized by  a  marked  resemblance  to  their  environment. 
Such  crustaceans  as  the  crawfish  and  Asellus,  such 
insects  as  Ephemerella,  Caenis  and  other  mayfly  nymphs 

Libellula,  Didymops, 
Celithemis  (fig.  200) 
and  other  dragonfly 
nymphs,  and  certain 
snails  and  flatworms 
belong  here. 

(2).  Bottom  dwel- 
lers that  descend  more 
or  less  deeply  into  the 
mud  or  sand,  by  the 
various  means  already 
discussed  in  the  pre- 
ceding  chapter. 
Among  the  shallow 
burrowers  are  many 
shell-bearing  molluscs, 
both  mussels  and 
snails;  a  few  may- 
fly and  dragonfly 
nymphs.  Descending 
more  deeply  in  muddy 
beds  are  some  true  worms  and  horsefly  larvae. 

The  shelter-building  forms  of  the  bottom  may  be 
grouped  as: 

(1).  Forms  making  portable  shelters.  These  are 
mainly  caddis-worms  that  construct  cases  of  pieces  of 
wood  or  grains  of  sand. 

(2).  Forms  making  fixed  shelters.  These  are 
such  caddis- worms  as  Polycentropus,  such  worms  as 
Tubifex  (see  fig.  83  on  p.  174)  and  such  midges  as 
Chironomus  (see  fig.  134  on  p.  220). 


Fig.  200.     A  bottom  sprawler:  nymph  of 

of  the  dragonfly,  Celithemis  eponina. 


Marsh  Societies  341 


It  is  some  of  these  animals  of  the  pond  bottom  that 
give  to  the  littoral  region  its  great  extension  out  under 
the  open  waters  of  the  lakes.  It  is  only  a  few  meml  n  ts 
of  the  population  that  are  able  to  endure  conditions  in 
the  depths  far  out  from  shores.      These  are  such  as: 

Small  mussels  of  genus  Pisidium. 

Mayfly  nymphs  of  the  genus  Hexagenia. 

Midge  larvae  of  the  genus  Chironomus. 

Caddis-worms  in  the  cylindric  cases  of  sand,  not  yet 
certainly  identified,  etc. 

The  larger  animals  of  the  pond  that  belong  neil 
to  surface  nor  bottom  and  that  correspond  to  neither 
plancton  nor  necton  of  the  open  water  may  be  grouped 
as: 

(i).  Climbing  forms  (most  of  which  can  swim  on 
occasion),  such  as  the  scuds  (Amphipods),  the  nymphs 
of  dragonflies  such  as  Anax,  of  damselflies  such  as  Lestes 
and  Ischnura,  of  mayflies  such  as  Callibaetis,  larvae  of 
caddisflies  such  as  Phryganea  and  of  moths  such  as 
Paraponyx,  mussels  such  as  Calyculina,  and  many 
leeches,  entomostracans  and  rotifers. 

(2).  Sessile  forms  such  as  hydras,  sponges,  bryz<  >ans 
and  rotifers. 

II 

Marsh   Societies. — We   come   now   to   consider   the 
associations  of  organisms  in  waters  that  are  not  too  deep 
for  the  growth  of  standing  aquatics.     Shoalness  of 
water  and  instability  of  temperature  and  other  phy  - 
conditions  at  once  exclude  from  residence  in  the  marsh 
the  plants  and  animals  of  more  strictly  limnetic  habits; 
but  it  is  doubtless  the  presence  of  dense  emergent  plant 
growth  that  most  affects  the  entire  population.     Tin 
gives  shelter  to  a  considerable  number  of  the  hi. 
vertebrates,  and  these  rather  than  the  fishes  are  the 
large   consumers    of   marsh   products.     The    muskrat 


342 


Aquatic  Societies 


breeds  here  and  builds  his  nest  of  rushes.  He  prefers, 
to  be  sure,  the  edge  of  a  marsh  opening,  where  in  deep 
water  he  may  find  crawfishes  and  molluscs,  with  which 
to  vary  his  ordinary  diet  of  succulent  shoots  and  tubers. 


Fig.  201.     The  eggs  of  the  spotted  salamander,  Ambystoma  punctatum. 

tPhoto  by  A.  A.  Allen.) 

Deep  in  the  marsh  dwell  water  birds,  such  as  grebes, 
rails,  coots,  terns,  bitterns,  and  in  the  north,  ducks  and 
geese  as  well.  Such  non-aquatic  birds  as  the  long-billed 
marsh-wren  and  the  red-winged  blackbird  use  the  top 
of  the  marsh  cover  as  a  place  to  build  their  nests  ami 


Marsh  Plants 


343 


use  also  the  leaves  of  marsh  plants  for  building  materials. 
Several  turtles  and  water  snakes  are  permanent 
dents  as  are  also  a  few  of  the  frogs.  Most  of  the  fr<  >gs 
visit  the  marsh 
pools  at  spawn- 
ing time,  making 
the  air  resound 
with  their  nup- 
tial melodies. 
The  spotted  sal- 
amander is  the 
earliest  amphi- 
bian to  spawn 
there.  Though 
the  adult  is  but 
a  transient,  its 
larvae  remain  in 
the  marsh  pools 
through  the  sea- 
son. 

The  plants  are 
the  same  kinds 
found  in  the 
marginal  zone  of 
the  pond  border, 
hut  here  they  of- 
ten cover  large 
areas  in  a  nearly 
pure  stand.  In 
our  latitude  in  the  more  permanent  waters,  the 
dominant  species  usually  are  cat-tail,  phragmites, 
bur-reed  and  the  soft-stemmed  bulrushes;  in  the 
shoals  that  dry  up  each  year  they  are  sweet  flag, 
sedges,  manna  grass  and  the  hard-stemmed  bul- 
rushes. Such  plants  as  these  have  strong  h 
laced  roots  and  runners  that  form  the  1  iasis  <  A  the  marsh 


Fig.  202.     Tear-thumb. 


344 


Aquatic  Societies 


cover,  and  that  support  a  considerable  variety  of  more 
scattering  species.  One  of  the  most  widespread  of 
these  secondary  forms  is  the  beautiful  marsh  fern, 
whose  black  rootstocks  over-run  the  tussocks  of  the 
sedges,  shooting  up  numberless  fronds.  Scattering 
semi-aquatic  representatives  of  familiar  garden  groups 
are  the  marsh  bellwort  {Campanula  a  paranoides),  the 
marsh  St.  John's  wort  (Hypericum  virginicum)  and  the 
marsh  skull-cap  (Scutellaria  galericulata) :  these  are 
dwarfish  forms,  however,  that  nestle  about  the  bases  of 
the  taller  clumps.  With  them  are  straggling  prickly 
forms,  such  as  the  marsh  bedstraw  (Galium  palustre), 
the  white  grass  (Leersia)  and  the  tear-thumb  (Polygo- 
num sagittal  urn,  fig.  202).  Strong  growing  forms  that 
penetrate  the  marsh  cover  with  stout  almost  vine-like 
stems  are  the  marsh  five-finger  (Potentilla  palustris)  the 


Fig.  203.   A  marshy  pool  with  flowers  of  the  white  water  crow-foot  rising 
from  the  surface. 


Marsh  Animals  34c 


joint  weed  {Polygonum)  and  the  buck-bean  (Menyan- 
thes  trifoliata).  True  climbers  also,  are  present  in  the 
marsh  although  usually  only  on  its  borders;  such  are 
the  climbing  nightshade  bittersweet  {Solatium  dulca- 
mara) and  the  beautiful  fragrant -flowered  climbing 
hemp-weed  (Mikania  scandens).  Here  and  there  one 
may  see  a  protruding  top  of  swamp  dock  (Rumex 
verticillatus) ,  a  water  hemlock  (Cicuta  bulb  if  era)  or  a 
swamp  milkweed  (Asclepias  incamata). 

Every  opening  in  the  marsh  contains  forms  that  are 
more  characteristic  of  ponds  and  ditches,  such  as  arr<  >w- 
heads  and  water  plantain.  And  even  the  little  trash 
filled  pools  often  contain  their  submerged  aquatics. 
Such  a  one  is  shown  in  the  figure  203,  a  shallow  pool 
filled  with  fallen  leaves,  its  surface  suddenly  sprinkled 
over  with  little  star-like  flowers  when  the  white  water- 
crowfoot  shoots  up  its  blossoms. 

Algae  often  fill  these  pools;  sometimes  minute  free- 
swimming  forms  that  tint  their  waters,  but  more  often 
''blanket  algae,"  whose  densely  felted  mats  may  smother 
the  larger  submerged  aquatics. 

The  animal  life  of  the  marsh  is  also  a  mixture  of  pond 
forms  and  of  forms  that  belong  to  the  more  permanent 
waters.  The  fishes  are  bullheads  and  top  minnows  and 
others  that  can  endure  foul  waters,  scanty  oxygen  and 
rapid  fluctuations  of  temperature.  Of  crustaceans, 
ostracods  and  scuds  are  most  abundant.  Of  molluscs, 
Pisidium  and  Planorbis  are  much  in  evidence,  and  other 
snails  are  common.  Insects  abound.  Some  are  aqua- 
tic and  some  live  on  the  plants.  Of  all  Odonata,  Lestes 
(fig.  204)  is  perhaps  the  most  characteristic  marsh  inhal  >i- 
tant;  of  mayflies,  Blasturus  and  Caenis ;  stoneflies,  then 
are  none.  Of  caddis-flies  there  are  many,  but  Limno- 
philus  indivisus  is  perhaps  the  most  characteristic  marsh 
species.     It  is  not  known  to  inhabit  any  waters  except 


346 


Aquatic  Societies 


those  that  dry  up  in  summer.  The  commonest  beetles 
are  small  members  of  the  families  Hydrophilidae, 
Dytiscidae  and  Haliplidae.     The  most  characteristic  of 

the  bugs  is  the  slen- 
der little  marsh- 
treader,  Limno- 
bates.  Swale-flies, 
mosquitoes,  crane- 
flies  and  ubiqui- 
tous midges  abun- 
dantly represent 
the  aquatic  Dip- 
tera. 

There  are,  of 
course,  many  in- 
sects dependent 
upon  particular 
plants.  Such  are 
the  tineid  moth, 
Limnacea  phragm  i- 
tella,  that  burrows 
when  a  larva  in 
the  Typha  fruit 
spike,  and  the  wee- 
vil, Sphenophorus, 
that  burrows  in  the 
Typha  crown;  the 
leaf -beetle,  Dona- 
tio, emerginata, 
whose  larva  feeds 
on  the  submerged  roots  of  the  bur-reed,  etc.  Here  are 
also  a  number  of  characteristic  spiders,  such  as  the 
diving  spider,  Dolomedes. 

Doubtless  the  lower  groups  of  animals  possess  species 
that  are  addicted  to  dwelling  in  marshes,  and  fitted  to 
the  peculiar  conditions  such  places  impose,  but  these 


1' 

• 

m\ 

X 

.  "I 

i 

V 

x 

1  1 

1 

Fig.  204.     A  damselfly.     Lestes  uncatus. 


Marsh  Societies 


347 


have  been  little  studied.     There  is  hardly  any  situati<  m 
where  the  fauna  is  so  imperfectly  known. 

As  compared  with  the  land,  fauna  and  flora  of 
marshes  are  characterized  by  a  small  number  of  species, 
and  enormous  numbers  of  individuals.     In  other  w< 


Fig.  205.     "Tree-swallow  pond":     a  once  famous  collecting  ground  in  th 
Renwick  marshes  at  Ithaca.     Photo  taken  in  spring  after  the  burning  and 
the  freezing  and  the  floods,  but  before  the  growth  of  the  season. 

the  population  is  one  of  small  variety  but  of  great  den- 
sity. Such  forms  as  are  fitted  to  maintain  themselves 
where  floods  and  fire  alternately  run  riot  find  in  the  rich 
soil  and  abundant  light  and  moisture  opportunity  fi  >r  a 
great  development.  Fire  sweeps  the  surface  clear  of 
trees,  which  would  overtop  and  overshadow  the 
herbage  and  would  create  swamp  conditions.  The 
ground  layer  of  water-soaked  trash  prevents  the  burn- 


348  Aquatic  Societies 


ing  of  the  root  stocks;  it  also  prevents  deep  freezing 
after  the  fires  have  run.  Plants  that  are  capable  of 
renewing  their  vegetative  shoots  from  parts  below  the 
level  of  the  burning,  are  the  ones  that  year  after  year, 
maintain  their  place  in  the  sun. 

Ill 

Bog  Societies.  Bogs  belong  to  moist  climates  and  to 
places  where  water  is  held  continuously  in  an  amount 
sufficient  to  greatly  retard  the  complete  decay  of  plant 
remains.  Acids  accumulate,  especially,  humous  acids. 
The  soil  becomes  poor  in  nutriment,  especially  in 
available  nitrogen.  Plants  can  absorb  little  water, 
at  least  at  low  temperature;  and  the  typical  bog 
situation  is  therefore  said  to  be  ''physiologically  dry." 
With  such  conditions  there  go  some  striking  differences 
in  flora  and  fauna.  The  plants  are  "oxylophytes"  like 
sphagnum  and  cranberry,  i.  e.,  plants  that  can  grow  in 
more  or  less  acid  media,  and  that  have  many  of  the 
superficial  characteristics  of  desert  plants;  such  as 
vestiture  of  hairs  or  scales  or  coatings  of  wax,  thickened 
cuticle,  leaves  so  formed  or  so  closed  together  as  to 
limit  or  retard  transpiration.  The  kinds  of  plants  are 
fewer;  the  individuals  crowd  prodigiously.  They  are 
eaten  by  animals  less  than  in  any  other  situation. 
Their  remains,  partly  decomposed,  are  added  to  the  soil 
in  the  form  of  deposits  of  peat.  The  animal  population 
is  correspondingly  reduced  and  scanty. 

Sphagnum.  The  most  characteristic  single  organism 
in  such  a  situation  is  the  bog-moss,  Sphagnum  (fig.  206; 
see  also  fig.  59  on  p.  147).  This  grows  in  cushion-like 
masses  of  soft  erect  unbranched  stems,  that  are  in- 
dividually too  weak  and  flaccid  to  stand  alone,  but  that 
collectively  make  up  the  largest  part  of  the  bog  cover. 
The  masses  are  loose  and  easily  penetrated  by  the  roots 


Sphagnum 


349 


and  runners  of  other  stronger  plants.  It  is  the  inter- 
penetration  of  these  that  binds  the  bog  cover  together 
making  it  resilient  under  foot. 

The  leaves  of  Sphagnum  are  interspersed  with  cells 
that  are  mere  water  reservoirs  having  porous  walls. 
Some  of  these  leaves  are  denexed  against  the  stem  and 
make  excellent  capillary 
conduits  for  water  upward 
or  downward.  Whether  the 
abundant  supply  be  in  the 
air  above  or  in  the  soil  be- 
low, these  make  provision 
for  the  equitable  distribu- 
tion of  it.  Wherefore,  these 
masses  of  sphagnum  become 
water  reservoirs,  holding 
their  supply  often  against 
gravity,  and  bathing  the 
roots  of  all  the  cover  plants 
that  rise  above  the  surface 
of  the  bog. 

Sphagnum  belongs  to  the 
shore,  and  it  is  quite  incap- 
able of  advancing  into  the 
water  unassisted.    But  with 

the  help  of  stronger  more  straggling  plants  whose  roots 
and  branches  penetrate  and  interlace  in  its  masses  in 
mutual  support,  it  is  able  to  extend  as  a  floating  border 
out  over  the  surface  of  still  water  in  small  lakes  and 
ponds.  These  floating  edges  may  be  depressed  by  the 
weight  of  a  man  until  they  are  under  water,  but  t hey 
are  tough  and  elastic,  and  rise  again  unbanned  when 
the  weight  is  removed.  Long,  strong,  pliant-stemmed 
heaths  and  slender  sedges  are  the  plants  commonly 
associated  with  sphagnum  in  the  making  of  this  floating 
border.  In  the  bog  cover  equally  close  is  its  ass(  »eiat  i<  >a 
with  the  common  edible  cranberry. 


Fig.  206.     Bog  moss,  Sphagnum; 

1  the  tip  of  a  spray;  b,  a  few  cells  from 
a  leaf ;  x,  long  interlaced  lines  of  slen- 
der sinuous  chlorophyl-bearing  cells, and 
y,  large  empty  water  reservoir  cells  hav- 
ing pores  in  their  walls  for  admission  of 
water  and  annular  cuticularisations 
for  support. 


00< 


Aquatic  Societies 


Some  habitual  associates  of  sphagnum  are  shown  in 
figure  207.  In  such  a  place  as  the  foreground  of  this 
picture,  if  one  slice  the  bog  cover  with  a  hay-knife,  he 


Fig.  207.  A  bit  of  bog  cover.  (AIcLean,  N.  Y.).  From  the  central  clump 
of  pitcher-plant  leaves  rises  one  long-stalked  flower.  The  surrounding  bog 
moss  is  Sphagnum.  A  few  slender  stems  of  cranberry  trail  over  the  moss. 
The  taller  shrubs  are  mainly  heaths  such  as  Cassandra  and  Andromeda. 


(Photo  by  II.  II.  Knight.) 


may  easily  lift  up  the  slices;  for  they  are  composed  of 
living  material  to  a  depth  of  only  about  a  foot.  Below 
is  peat ;  at  first  light  colored  and  composed  of  identifi- 
able plant  remains,  but,  deeper,  becoming  darker  and 
more  completely  disintegrated.     The  slices  cut  from 


Bog  Plants 


.-o 


the  surface  have  sphagnum  for  their  filling,  but  they 
tough  and  pliant,  like  strips  of  felt,  owing  to  the  i 
interlacing  of  roots  and  stems  of  the  other  plants  of  the 
bog  cover. 

Many  delightful  herbs  grow  on  the  surface  of  the  1 
The  pitcher-plant  shown  in  our  figure  is  one,  and  the 

sundew  (see  fig.  172  on  p. 
283)  is  another  carnn 
ous  species.  These,  as  we 
have  seen  in  the  preceding 
chapter,  have  their  own 
way  of  getting  nitrogen  when 
the  available  supply  is  small. 
Orchids  of  several  genera 
(Habenaria,  etc.)  and  moc- 
casin flowers  (fig.  208)  there 
bear  beautiful  flowers.  Cot- 
ton grass  (Eriophorum)  is 
showy  enough  with  its  white 
tufts  held  aloft  when  in 
fruit,  and  a  beaked  rush 
(Rynchospora)  is  its  natural 
associate.  In  places  where 
the  surface  rises  in  little 
hummocks,  there  are  apt  to 
&  be  patches  of  the  xerophytic 

moss,  Polytrichium,  associ- 
ated with  charming  little 
colonies  of  wintergreen  and 
goldthread.  At  the  rear 
of  the  heath  shown  in  our  figure  stand  huckleberries 
bog  brambles  and  masses  of  tall  bog  ferns  while  thickets 
of  alder  and  dogwood  crowd  farther  back. 

Where  sphagnum  borders  on  open  water,  there  often 
lies  in  front  of  it  the  usual  zone  of  aquatics  with  ll<  mating 
leaves,  as  shown  in  the  accompanying  picture,  and  m 


Fig.  208.  A  charming  bog  plant, 
the  moccasin  flower.  (Cypri- 
pedium  reginae). 


Aquatic  Societies 


still  deeper  water  there  are  apt  to  be  beds  of  Chara  and 
of  pondweeds.  These  and  the  molluscs  associated 
with  them,  leave  their  calcified  remains  deposited  on 
the  pond  bottom  as  a  stratum  of  marl.     Thus  the 


Fig.  209.     Mud  pond,  near  McLean,  N.  Y.     This  is  a  bog  pond,  surrounded 
in  part  at  least  by  floating  sphagnum.     The  outlet  (to  left  in  the  picture)  is 
bordered  by  tussock  sedges,  backed  up  by  extensive  alder  thickets. 
(Photo  by  John  T.  Needham.) 

filling  of  a  bog  pond  is  in  time  accomplished  by  the 
deposition  of  a  layer  of  marl  over  its  bottom,  and  a 
much  thicker  mass  of  peat  over  the  marl.  Successive 
stages  in  the  filling  process  are  graphically  shown  in 
Dachnowski's  diagram,  copied  on  the  next  page. 

Peat  formation  and  filling  of  beds  goes  on,  of  course,  in 
ponds  where  there  is  no  sphagnum;    goes  on  wherever 


Peat  and  Marl 


353 


the  conditions  for  incomplete  decay  of  plants  prevail; 
and  from  the  foregoing  it  will  be  seen  that  peat  is  n<  it 
likely  to  be  composed  of  the  remains  of  sphagnum 
alone.  The  forefront  of  advancing  shore  vegetation  is 
led  by  a  number  of  plants  of  very  different  character. 


Bf        Bs  Bm         5      M        O-W 


Bf  Bs.Bm 


*&&?'■'     ■  • 


- - 


Fig.  210.  Dachnowski's  diagram  illustrating  three  stages  in  the  filling 
of  a  pond  with  deposits  of  peat  and  marl.  Peat  is  stippled;  marl, 
cross-lined. 

OW,  open    water;     M,  marginal  succession;     S.  shore  succession;    B.    b 

including  bog  meadow  (Bm),  bog  shrub  (Bs),  and  bog  forest  (Bli;     MP,  mesophylic 
forest. 


354 


Aquatic  Societies 


The  accompanying  diagram 
shows  five  modes  of  progress  into 
deeper  water  of  pioneer  land- 
building  plants. 

a  is  the  method  of  the  spike- 
rush  on  gently  sloping  shore.  It 
is  the  method  by  which  number- 
less shore  plants  extend  their  hold- 
ings,— subterranean  off-shoots. 

b  is  the  method  of  the  tussock 
sedges  (see  also  fig.  209)  which  on 
the  loose  mud  in  shallow  waters 
build  up  solid  clumps.  Many  of 
these,  less  than  a  foot  in  diameter, 
are  yet  of  such  firmness  that  they 
will  sustain  the  weight  of  a  man. 
Every  one  knows  such  clumps, 
from  having  used  them  (as  step- 
ping stones  are  used)  in  crossing 
a  swale.  New  offsets  lie  hard 
against  the  old  ones,  roots  descend 
in  close  contact,  and  fibrous  root- 
lets interlace  below  in  extraordin- 
ary density. 

c  is  the  method  of  the  swamp 
loosestrife,  Decodon,  a  method  of 
advancing  by  long  single  strides. 
The  tips  of  the  long  over-arching 
shoots  dip  into  the  water,  and 
then  develop  roots  and  buds  and 
a  copious  envelope  of  aerating  tis- 
sue.    If  these  new  roots  succeed 


Fig.  211.  Diagram  illustrating  the  method  of 
advance  into  deeper  waters  of  typical  land- 
building  plants. 

a.  Spike    rush;     b,    tussock    sedge;    c,    swamp    loose- 
strife;   d,  cat-tail  flag;    e,  Sphagnum  and  hea  tn   s. 


Land-building  Plank 


303 


in  taking  a  good  hold  on  the  bottom,  then  other  shoots 
spring  from  this  new  center  and  repeat  the  process 

d  is  the  method  of  the  cat-tail  flag.  It  consist  in 
developing  an  abundance  of  interlaced  fibrous  roots 
and  then  simply  floating  on  them.  Much  mutual  sup' 
port  is  required  by ^plants  that  grow  so  tall;  and  any 
great  advance  of  a  few  clumps  beyond  the  general  front 
may  result  in  disaster  from  overturn  by  winds 

eis  a  method  of  mutual  support  between  sjiecies  of 
very  different  sorts.  It  is  that  of  the  sphagnum  and 
heaths  just  discussed.  Greater  progress  over  deeo 
water  is  made  by  this  method  than  bv  any  of  the  oth<  srs 

A  photograph  of  the  first  named  is  "reproduced  as 
figure  212. 


Fig.  212.     A  bit 

of  running 
root-stock  of 
a  spike  rush. 
Eleo  charts 
p  a  I  u  s  tris, 
showing  its 
method  of  ad- 
vance over  the 
pond  bottom. 
Bra  nching 
subterranean 
off-shoots  ex- 
tend down  a 
sloping  shore 
until  t  h  e  y 
reach  a  depth 
of  water  in 
which  they 
cannot  func- 
tion  effec- 
tively. 


356  Aquatic  Societies 


IV 

The  population  of  stream  beds — If  we  distinguish 
between  lenitic  and  lotic  societies  by  presence  or 
absence  of  growths  of  vascular  plants,  then  the  greater 
part  of  stream  beds  shelter  lenitic  societies.  The 
greater  part  has  not  a  current  of  sufficient  swiftness  to 
prevent  the  growth  of  such  plants.  And  indeed  it  is 
only  in  restricted  portions  of  any  stream  that  we 
find  the  animals  specially  adapted  to  meet  conditions 
imposed  by  currents. 

Where  the  stream  bed  forms  a  basin,  there  the  condi- 
tions of  life,  for  the  larger  organisms  at  least,  approxi- 
mate those  of  a  lake.  Hence  we  find  in  those  places 
in  large  streams  where  the  water  is  deep  and  still,  there 
occur  many  forms  like  those  in  lakes.  The  sturgeon 
belongs  in  both,  and  so  do  the  big  mussels  and  the 
operculate  snails,  the  big  burrowing  mayflies,  the  big 
tube  dwelling  midge  larvae,  etc.  The  basins  of  creeks 
offer  conditions  like  those  in  ponds;  the  basins  of 
brooks,  conditions  like  those  of  pools.  And  the  largest 
species  are  restricted  to  such  of  the  larger  basins  as  can 
afford  them  adequate  pasturage  and  suitable  places  for 
rearing  their  young.  To  be  sure,  in  all  those  basins, 
the  water  is  constantly  passing  on  down  stream  and 
the  plancton  of  the  basin,  while  in  part  developing  there, 
is  in  a  large  part  constantly  lost  below  and  constantly 
renewed  from  above.  Kofoid  (08)  states  that  'The 
plancton  of  the  Illinois  River  is  the  result  of  the 
mingling  of  small  contributions  by  tributary  streams, 
largely  of  littoral  organisms  and  the  quickly  growing 
algae  and  flagellates,  and  of  the  rich  and  varied  plancton 
of  tributary  backwaters,  present  in  an  unusual  degree 
in  the  Illinois  because  of  its  slightly  developed  flood- 
plain,  and  from  which  it  is  never  entirely  cut  off,  even 
at  lowest  water.  *  *  *  *  To  these  elements  is  added 
such  further  development  of  the  contributed  or  indigen- 


The  Population  of  Stream  Beds  jey 

ous  organisms  as  time  permits,  or  the  special  conditions 
of  nutrition  and  sewage  contamination  facilitate. 
Though  continually  discharging,  the  stream  maintains 
the  continuous  supply  of  plancton,  largely  by  virtu 
the  reservoir  backwaters — the  great  seedbeds  from 
which  the  plancton-poor  but  well  fertilized  contribu- 
tions of  tributary  streams  are  continuously  sown  with 
organisms  whose  further  development  produces  in  the 
Illinois  River  a  plancton  unsurpassed  in  abundance." 

Doubtless,  in  every  stream  the  plancton  supply  is 
constantly  renewed  from  sheltered  and  well  populated 
basins,  which  serve  as  propagating  beds.  And,  indeed, 
on  every  solid  support  diatoms  are  growing,  and  the 
excess  of  their  increase  is  constantly  being  released 
into  the  passing  current.  In  the  swiftly  flowing, 
plancton-poor  streams  about  Ithaca  there  is  not  time 
for  much  increase  of  free  planctons  by  breeding.  The 
waters  run  so  swift  a  course  they  can  only  carry  into 
the  lake  such  forms  as  they  have  swept  from  their 
channels  in  their  rapid  descent. 

While  there  has  been  much  study  of  the  life  of  the 
open  waters  of  rivers  there  has  hitherto  been  little 
study  of  their  beds.  Where  the  beds  are  sandy  with 
flow  of  water  over  them  we  know  the  life  differs  from 
that  of  muddy  basins.  The  heavier-shelled  mussels  an<  1 
snails  are  on  the  sand;  and  the  commoner  insects  there 
are  the  burrowing  nymphs  of  mayflies  and  Gomphine 
dragon-flies,  and  the  caddis-worms  that  live  in  portable 
tubes  of  sand. 

The  beds  of  the  smallest  streams  are  easy  of  ac« 
and  a  few  observations  are  available  to  indicate  that 
their  study  will  bring  to  light  some  interesting  eo  >1<  >gical 
relations.     A  few  very  restricted  situations  will  be  cited 
in  illustration. 


:,5* 


I  qua  tic  Societies 


Moss  patches — On 
the  rocky  beds  of 
large  brooks  that  run 
low  but  do  not  en- 
tirely run  dry,  there 
are  frequent  patches 
of  the  close-growing 
moss,  Hydrohyp- 
num.  These  patches 
frequently  cover  the 
vertical  face  of  a 
waterfall  (fig.  213). 
The  little  water  that 
remains  in  dry  season 
trickles  through  the 
layer  of  moss,  and 
in  times  of  flood  the 
speedier  torrent 
jumps  over  it.  Under 
the  flattened  frond- 
like green  sprays 
there  is  compara- 
tively quiet  water 
at  all  times;  and  in 
this  situation  there 
lives  a  peculiar  as- 
semblage of  insects 
that  differ  utterly 
from  the  lotic  forms 
dwelling  in  the  same  streams  (to  be  discussed  in  a  later 
part  of  this  chapter),  tho  often  dwelling  within  a  few 
feet  of  them.  They  lack  all  the  usual  adaptations  for 
meeting  the  wash  of  currents.  They  are  (with  occa- 
sional intermixture  of  a  few  larvae  of  small  midges 
and  of  Simulium)  the  following: 


FlG.  213.  A  moss-bed  covering  the  face  of  a 
rock  ledge  (in  flood  time,  a  waterfall)  in 
the  bed  of  Williams  Brook  at  Ithaca, 
\.  V.  The  water  seen  on  the  rock  above 
trickles  down  through  this  moss.  Here 
restricted  and  peculiar  animal  pop- 
ulation. 


Moss  Inhabitants 


359 


1.  The  slender  larvae  of  soldier-flies  (Euparhyphus 
brevicornis) .  Each  bears  a  pair  of  ventral  hooks  that 
may  serve  for  attachment. 

2.  The  greenish  larvae  of  the  cranefly  (Dicrano- 
myia  simidans). 

3.  The  warty-backed  larvae  of  the  Parnid  beetle 
{Elmis  quadrinotatus) . 

4.  Larvae  and  pupae  of  a  little  black  Anthomyid  fly 
(Limnophora  sp.?). 


Fig.  214.  Insect  larvae  from  a  moss  patch  such  as  is  shown  in  the 
preceding  figure,  a,  Psychoda;  b,  Elmis;  c,  d,  e,  Euparhyphus,  c, 
being  lateral,  d,  dorsal  and  e,  ventral  views,  c  and  e  show  the  huge 
ventral  hooks  on  the  penultimate  segment ;  /  and  g,  cases  of  an  un- 
known caddis-worm,  /,  composed  mainly  of  sand;  g,  mainly  of  moss. 


360 


Aquatic  Societies 


5.  The  slender  larvae  of  a  moth  fly  (Psychoda  alter- 
nate), its  body  covered  with  deflexed  spines. 

6.  The  larvae  of  an  unknown  caddis-fly  whose  cases 
are  composed  sometimes  of  stones,  sometimes  of  moss 

fragments. 


Leaf -drifts — -In  the  beds  of  wood- 
land brooks,  there  are  barriers  of 
fallen  leaves,  piled  by  the  current 
upon  the  bare,  obtruding  roots  of 
trees.  These  leaf -drifts  have  a 
population  of  their  own,  the  most 
charactertistic  member  of  which 
about  Ithaca  is  the  huge  larva 
shown  in  figure  215.  This  is  the 
larva  of  the  giant  cranefly,  Tipula 
abdominalis.  Associated  with  this 
larva  in  these  water-soaked  masses 
of  leaves,  are  the  nymphs  of  such 
stoneflies  as  Nemoura  and  of  such 
mayflies  as  Baetis  and  Leptophle- 
bia,  a  few  beetles  and  often  many 
scuds  (Gammarus).  In  the  mud 
behind  the  leaf -drifts,  there  are 
often  earthworms,  washed  down 
from  fields  above. 

In  the  clear  pools  in  upland 
streams  that  flow  through  swampy 
woods,  when  the  bottom  is  strewn 
with  forest  litter  intermixed  with  brownish  silt,  there 
dwell  a  number  of  forms  that  certainly  belong  totheleni- 
tic  rather  than  to  the  lotic  societies.  Such  are  the  caddis- 
worms  of  figure  216.  With  these  are  associated  small 
mussels  of  the  genus  Sphaerium,  squat  dragonfly 
nymphs  of  the  genus  Cordulegaster,  and  climbing 
nymphs  of  the  genus  Boyeria,   water-skaters  on  the 


Fig.  215.  Two  larvae  of 
tin-  giant  cranefly,  Tip- 
ula abdominalis,  an  in- 
habitant of  leaf-drifts  in 
woodland  brooks. 

Natural  size. 


Leaf-drifts 


36 


surface  and  burrowing  mayflies  in  the  beds,  and  a  con- 
siderable variety  of  the  lesser  midges  on  every  possible 
support. 


Fig.  216.  A  bit  of  the  bed  of  a  pool  in  a  woodland  stream,  show-] 
ing  among  the  forest  litter  the  wooden  cases  of  the  larva  of  the 
caddis-fly,  Halesus  guttifer.  (See  also  fig.  104  on  p.  198).  Pro- 
tective resemblance.     There  are  14  cases  in  the  picture. 


LOTIC 
DCIETIES 


CCORDING  to  the 
grouping  outlined  on 
page  315,  we  designate 
by  this  name  those  as- 
semblages of  organisms 
that  are  fitted  for  life 
in  rapidly  moving  water 
— that  are  washed  by 
currents,  as  the  name 
signifies.  Whether  the 
water  flow  steadily  in 
one  direction  as  in 
streams,  or  back  and 
forth  with  frequent  shifts  of  direction  as  on  wave- 
washed  shores,  the  organisms  present  in  it  will  be  much 
the  same  sorts.  The  plants  will  be  mainly  such  algae 
as  Cladophora,  and  slime-coat  diatoms:  the  animals 
will  be  mainly  net-spinning  caddis-worms  and  a  variety 
of  more  or  less  limpet-shaped  invertebrates. 

The  animals  of  lotic  societies  are  mainly  small  inver- 
tebrates. There  are  fishes,  indeed,  like  the  darters  that 
live  in  the  beds  of  rapid  streams.  These  lie  on  the 
bottom  where  the  current  slackens,  lightly  poised  on 
their  large  pectoral  fins,  or  rest  in  the  lee  of  stones, 
darting  from  one  shelter  to  another.     It  is  only  a  few 


363 


364  Aquatic  Societies 


lesser  animals,  of  highly  adapted  form  and  habits,  that 
are  able  to  dwell  constantly  in  the  rush  of  waters. 

These  lesser  animals  may  be  roughly  divided  into  two 
categories  according  to  the  sources  of  their  principal 
food  supply: 

1 .  Plancton  gathering  forms,  that  are  equipped  with 
an  apparatus  for  straining  minute  organisms  out  of  the 
open  current. 

2.  Ordinary  forms  that  gather  home-grown  food 
about  their  dwelling  places. 

1.  Plancton  Gatherers. — These  are  they  that  live 
mainly  on  imported  food,  which  by  means  of  nets  or 
baskets  or  strainers  they  gather  out  of  the  passing 
current.  These  are  the  most  typical  of  lotic  organisms, 
for  they  must  needs  live  on  the  exposed  surfaces  that 
are  washed  by  the  current.  They  dwell  on  the  bare 
rock  ledge,  over  which  the  water  glides  swiftly,  or  on  the 
top  of  the  boulders  in  the  stream  bed,  or  on  the  exposed 
side  of  the  wrave-washed  pier.  They  are  few  in  kinds, 
and  very  diverse  in  form,  and  show  many  signs  of 
independent  adaptation  to  life  in  such  situations. 
Among  them  are  four  that  occur  abundantly  in  the 
Ithaca  fauna.  These  four  and  their  mode  of  attach- 
ment and  of  plancton  gathering  are  illustrated  in  the 
accompanying  diagram.  The  fly  larva,  Simulium, 
adheres  by  a  caudal  sucker,  gathers  plancton  by  means 
of  a  pair  of  fans  placed  beside  its  mouth,  while  its  body 
dangles  head  downward  in  the  stream.  The  larva  of 
the  caddis-fly,  Hydropsyche,  lives  in  a  tube  and  con- 
structs a  net  of  silk  that  strains  organisms  out  of  the 
water  running  through  it.  The  caddis-worm,  Brachy- 
centrus,  attaches  the  front  end  of  its  case  firmly  to  the 
top  of  a  boulder  in  the  stream  bed,  and  then  spreads  its 
bristle-fringed  middle  and  hind  feet  widely  to  gather  in 
any  organisms  that  may  be  adrift  in  the  passing  water. 


Plancton  Gatherers 


36= 


The  nymph  of  the  "Howdy"  Mayfly,  Chirotenetes,  fixes 
itself  firmly  with  the  stout  claws  of  its  middle  and  hind 
feet  clutching  a  support,  and  extends  its  long  fore  feet 
with  their  paired  fringes  of  long  hair  outspread  like  a 
basket  to  receive  what  booty  the  current  may  bring. 
These  four  are  so  different  they  are  better  considered 
a  little  further  separately. 

The  larva  of  Simulium  (the  black-fly,  or  buffalo  gnat) 
perhaps  the  most  wide-spread  and  characteristic  animal 


Fig.  217.  Planet  on-gathering  insects 
of  the  rapids.  The  arrow  indicates 
direction  of  stream -flow. 


of  running  water,  is  unique  in  form  and  in  habits.  It 
hangs  on  by  means  of  a  powerful  sucker  that  is  located 
near  the  caudal  end  of  its  soft  and  pliant  bag-shaped 
body.  But  it  may  also  attach  itself  to  the  stones  by  a 
silken  thread  spun  from  its  mouth:  and  if  it  then 
loosens  its  sucker,  it  will  dangle  at  the  end  of  the  thread, 
head  upstream.  By  means  of  these  two  attachments, 
it  may  travel  from  place  to  place  without  being  washed 
away,  but  in  the  swiftest  water,  it  can  make  only  short 
moves  sidewise.  It  travels  by  loopings  of  its  body,  like 
a  leech.  So  it  shifts  its  location  with  changes  of  water 
level,  always  seeking  the  most  exposed  ledges  which  a 
thin  sheet  of  water  pours  over.  There  it  gathers  in 
companies,  so  closely  placed  side  by  side  as  to  form 
great  black  patches  on  the  stones. 


366  Aquatic  Societies 

There  is  little  movement  from  place  to  place.  The 
larva?  hang  at  full  stretch,  their  pliant  bodies  swaying 
with  little  oscillations  of  the  current,  their  fans  out- 
spread, straining  what  the  passing  stream  affords. 
Each  of  these  fans  is  composed  of  several  dozen  slender 
rays,  each  one  of  which  is  toothed  along  one  margin 
like  a  comb  of  microscopic  fineness,  and  all  have  a 
parallel  curvature  like  the  fingers  of  an  old-fashioned 
reaper's  cradle.     They  are  efficient  strainers. 

When  grown  the  larva  spins  its  half  cornucopia- 
shaped  straw-yellow  cocoon  on  the  vertical  face  of  a 
ledge  where  the  water  will  fall  across  its  upturned  open 
end,  then  transforms  to  a  pupa  inside.  The  pupa  bears 
on  the  prothorax  a  pair  of  long,  conspicuous,  many 
branched  respiratory  horns,  or  "tube  gills"  (see  fig.  171 
on  p.  280). 

The  eggs  are  laid  at  the  edge  of  the  swiftly  flowing 
water  on  any  solid  support,  on  the  narrow  strip  that  is 
kept  wet,  and,  by  oscillations  of  the  current  occasionally 
submerged. 

Hydro  psyche,  the  seine  making  caddis-worm,  lives  in 
sheltering  tubes  of  silk,  spun  from  its  own  silk  glands, 
fixed  in  position  on  the  surface  of  a  stone  (oftenest  in 
some  crevice) ,  and  covered  on  the  outside  with  attached 
sticks  or  broken  fragments  of  leaves  or  stones.  Always 
one  end  of  the  tube  is  exposed  to  the  current,  and  at 
this  end,  the  larva  reaches  out  to  forage.  Here  it  con- 
structs its  net  of  crosswoven  threads  of  fine  silk.  The 
net  is  a  more  or  less  funnel-shaped  extension  of  silk  from 
the  front  of  the  dwelling-tube.  The  opening  is  directed 
upstream,  so  that  the  current  keeps  it  fully  distended. 
The  semi-circular  front  margin  is  held  in  place  by 
means  of  extra  staylines  of  silk.  The  mesh  is  rather 
open  on  the  sides,  but  on  the  bottom  there  is  usually  a 
small  feeding  surface  that  is  much  more  closely  woven. 


Plancton  Gatherers 


367 


The  larva  lies  in  its  tube  in  readiness  to  seize  anything 
the  current  may  throw  down  upon  its  feeding  surface 
or  entangle  in  the  sides  of  its  net.  The  whole  net  is  so 
delicate  that  it  collapses  on  removal  from  the  water. 
To  see  it  in  action,  it  is  best  examined  through  a 
"water-glass."* 

Brachycentrus,  the  "Cubist"  caddis-worm,  is  re- 
stricted in  habitat  to  spring-fed  streams  flowing 
through  upland  bogs.  It  constructs  a  beautiful  case 
that  is  square  in  cross-section.  Each  side  is  covered 
with  a  single  row  of  sticks  (bits  of  leaf  stalks,  grass 
stems,  etc.)  placed  crosswise.  The  larva  fastens  its 
case  by  a  stout  silken  attachment  to  the  top  of  some 
current-swept  boulder  and  then  rests  with  legs  out- 
spread as  indicated  in  figure  217  in  a  receptive  atti- 
tude, waiting  for  whatever  organic  materials  the  current 
may  bring  within  its  grasp. 

The  Nymph  of  Chirotenetes,  the  " Howdy"  Mayfly,  lives 
on  the  rock  ledge  or  where  the  water  sweeps  among  the 
stones.  Its  body  is  of  the  stream-line  form  discussed 
in  the  last  chapter — the  form  best  adapted  to  diminish- 
ing resistance  to  the  passage  of  water,  as  well  when  at 
rest  as  when  swimming.  The  nymph  sits  firmly  on  its 
middle  and  hind  feet.  Holding  its  front  feet  forward,  it 
allows  the  current  to  spread  out  their  strainer-like 
fringes  of  long  hairs.  These  retain  whatever  food  is 
swept  against  them,  and  the  mouth  of  the  nymph  is 
conveniently  near  at  hand.  It  uses  its  feet  for  stand- 
ing but  moves  from  place  to  place  by  means  of  swift 
strokes  of  its  finely  developed  tail  fin,  supplemented  by 
synchronous  backward  strokes  of  its  strong  tracheal  gill 
covers.  It  has  almost  the  agility  and  swiftness  of  a 
minnow. 


*A  "water-glass"  is  any  vessel  having  opaque  sides  and  a  glass  bottom,  of 
convenient  size  for  use.  An  ordinary  galvanized  water  pail  with  its  bottom 
replaced  by  a  circular  glass  plate  set  nearly  flush,  is  excellent. 


368  Aquatic  Societies 


2.  Ordinary  Foragers. — These  are  the  members  of 
lotic  societies  that  lack  such  specialized  means  of 
gathering  food  from  the  passing  current,  and  that  forage 
by  more  ordinary  methods.  They  live  for  the  most 
part  on  the  sides  of  stones  and  underneath  them,  and 
not  on  their  upper  surfaces.  These  also  live  where  the 
water  runs  swiftly,  and,  for  the  most  part,  out  of  the 
reach  of  those  fishes  that  invade  the  rapids.  There  are 
two  principal  categories  among  them:  a.  Free-living 
forms  that  are  more  or  less  flattened  or  limpet -shaped. 
b.  Shelter-building  forms,  that  are  in  shape  of  body 
more  like  the  ordinary  members  of  their  respective 
groups. 

a 

The  limpet-shaped  forms  are  members  of  several 
orders  of  insects,  worms  and  snails.  Th^rr  flattened 
form  and  appressed  edges  are  doubtless  adaptations  to 
life  in  currents.  vThey  adhere  closely,  and  are  on 
account  of  their  form,  less  likely  to  be  washed  away; 
the  current  presses  them  against  the  substratum. 

Not  the  most  limpet-like  but  yet  the  best  adapted 
for  hanging  on  to  bare  stones  in  torrents  is  the  curious 
larva  of  the  net-veined  midge,  Blepharocera  (see  fig.  159 
on  p.  259),  an  inhabitant  only  of  clear  and  rapid  streams. 
The  depressed  body  of  this  curious  little  animal  is 
equipped  with  a  row  of  half  a  dozen  ventral  suckers, 
each  of  which  is  capable  of  powerful  and  independent 
attachment  to  the  stone.  So  important  have  these 
suckers  become  that  the  major  divisions  of  the  body 
conform  to  them  and  not  to  the  original  body  segments. 
On  these  suckers,  used  as  feet,  the  larva  walks  over  the 
stones  under  the  swiftest  water,  foraging  in  safety  where 
no  enemy  may  follow. 

Most  limpet-like  in  form  of  all  is  the  larva  of  the 
Parnid  beetle,    Psephenus,    commonly   known   as   the 


Ordinary  Foragers 


369 


"water-penny"  (see  fig.  160  on  p.  260).  It  is  nearly 
circular  and  very  flat  with  flaring  margins  that  fit  down 
closely  to  the  stone.  It  adheres  closely  and  is  easiest 
picked  up  by  first  slipping  the  edge  of  a  knife  under  it. 
Viewed  from  above,  it  has  little  likeness  to  an  ordinary 
beetle  larvae,  but  removed  from  the  stone  and  over- 
turned, one  sees  under  the  shell  a  free  head,  a  thorax 
with  three  short  legs,  an 
abdomen  and  some  minute 
soft  white  segment  ally 
arranged  tracheal  gills  on 
each  side. 

Other  insect  larvae  that 
have  taken  on  a  more  or 
less  limpet-like  form,  are 
the  nymphs  of  certain  May- 
flies and  of  many  stoneflies 
(fig.  in  on  p.  204).  The 
body  is  strongly  depressed. 
The  lateral  margins  of  the 
head  and  thorax  are  ex- 
tended to  rest  down  on  the 
supporting  surface.  The 
legs  are  broadened  and  are 
laid  down  flat  so  as  to 
offer  less  resistance  to  the 
currents,  and  stout  grap- 
pling claws  are  developed 
upon  all  the  feet.  Such  is 
Heptagenia  whose  nymphs 
abound  in  every  riffle  and 
on  every  rocky  shore. 
One  may  hardly  lift  a  stone  from  swift  water  and 
invert  and  examine  it  without  seeing  them  run  with 
sidelong  gait  across  its  surface,  outspread  flat,  and 
when  at  rest  appearing  as  if  engraven  on  the  stone. 


Fig.  218.  The  nymph  of  a  may- 
fly    (Heptagenia)    from     the 
rapids,  showing  depressed  form 
of  the  body  and  legs. 
(Photo   by  Anna  H.  Morgan.) 


370 


Aquatic  Societies 


The  head  is  so  flat  and  flaring  that  the  eyes  appear 
dorsal  in  position  instead  of  lateral  as  in  pond-dwelling 
Mayfly  nymphs. 

A  more  remarkable  form  is  the  torrent-inhabiting 
nymph  of  Rithrogena  whose  gills  are  involved  in 
the  flattening  process.  They  also  are  flattened  and 
extended  laterally  and  rest  against  the  stone.     But, 


FlG.  219.  The  nymph  of  an  unknown  mayfly  from  mountain 
torrents,  showing  oval  ventral  attachment-dise  formed  be- 
neath the  body. 

most  remarkable  of  all,  the  anterior  pair  is  deflected 
forward  and  the  posterior  pair,  backward,  to  meet  on 
the  median  line  beneath  the  body,  and  both  are 
enlarged  and  margined;  By  the  close  overlapping 
of  all  the  gills  of  the  entire  series  there  is  formed  a  large 
oval  attachment-disc  of  singularly  limpet-like  form. 

A   similar   flat    attachment-disc   is   formed    on    the 
ventral  side  of  the  mayfly  nymph  shown  in  figure  219, 


Shelter -building  Forms  371 

but  on  a  wholly  different  plan.  The  gills  are  not 
involved  in  the  disc,  but  instead  the  body  itself  is 
flattened  and  shaped  to  an  oval  form  underneath,  and 
fringed  with  close  set  hairs. 

There  is  in  the  mayflies  a  rather  close  correlation 
between  the  degree  of  flattening  of  the  body  and  the 
rate  of  flow  of  the  water  inhabited.  It  is  well  illus- 
trated by  the  allies  of  Heptagenia;  also  by  those  of 
Ephemerella,  among  which  occur  swift-water  forms. 
Epeorus,  Iron  and  Rithrogena  form  an  adaptive  series. 
Among  the  Parnid  beetles,  Elmis  (fig.  214b),  Dryops 
and  Psephenus  (fig.  160)  form  a  parallel  series. 

There  are  snails  that  dwell  in  the  rapids.  The  most 
limpet-shaped  of  these  is  Ancylus  (fig.  160  on  page  260) 
whose  widely  open  and  flaring  shell  has  in  it  only  a 
suggestion  of  a  spiral.  Certain  other  snails  (such  as 
Goniobasis  livescens)  are  of  the  ordinary  form  and  are 
able  to  maintain  themselves  on  the  stones  by  means  of 
a  very  stout  muscular  closely-adherent  foot.  Simi- 
larly, a  number  of  flatworms,  that 
adhere  closely  are  found  creeping 
in  the  rapids. 

Shelter -building  foragers  are  num- 
erous in  individuals  but  few  in 
kinds.  One  tube-dweller,  Hy- 
dropsy che,  is  a  plancton  gatherer 
and  has  been  already  discussed. 
There  are  other  shelter  building 
caddis-worms  living  among  stones 
in  running  water.  Ryacophila  fig.  220.  Two  pupal 
builds  at  close  of  larval  life  a  barri-        £?ses  of  the  caddis-fly 

1  ~  -  ...         ~  Kyacophila,    removed 

cade  of  stones  as  shown  in  the  ng.        from  the  stones. 
125  on  page  217,  and  shuts  itself  in 
and  spins  about  itself  a  brownish  parchment-like  c<  >c<  ><  >n 
of  the  form  shown  in  the  accompanying  figure.     Heli- 
copsyche    constructs    a    spirally    coiled    case    that    is 


372 


Aquatic  Societies 


strikingly  like  a  snail  shell,  and  fastens  it  down  closely 
in  the  shallow  crevices  of  stones  on  exposed  surfaces. 


H* 


Fig.  221.     The  spirally  coiled  cases  of  the 
caddis-worm,  Helicopsyche. 

A  number  of  other  caddis- worms  build  portable  cases 
of  sand  and  stones.  Those  of  Gcera  (fig.  222)  are 
heavily  ballasted  by  means  of  stones  attached  at  the 
sides  with  silk.     These  lie  down  flat  against  the  bottom 

and  doubtless  serve  the 
double  purpose  of  de- 
flecting the  current  and 
preventing  the  case  from 
being  washed  away. 

The  tubes  of  the  midges 
are  here  made  of  less 
soft  and  flocculent  ma- 
terials than  in  still 
waters.  T  any  tarsus 
makes  an  especially 
tough  case  of  a  pale 
brownish  color,  like  dried 
grass.  It  is  of  tapering 
form,  and  easily  recog- 
nized by  the  three  stay 
lines  that  run  out  from 
the  open  forward  end. 
p.,  c+      u  11    ,.  a  c     A  small  greenish  yellow 

ru,.    222.       Stone-ballasted    cases   of        .,  .^  ,      J    - 

caddis-worms  of  the  genus  Gcera.  larva    With    rather    long 


U% 


Limpet-shaped  Shelters 


373 


antennas  lives  within,  and  protrudes  its  pliant  length 

in  foraging  on  the  algal  herbage  that  grows  about  its 

front  door.  And 

there  are  many 

other     lesser 

midges    whose 

larvae    dwell    in 

silt  -  cover  e  d 

tubes   on   rocks 

in    the    rapids. 

Often  they  occur 

so  commonly  as 

to  almost  cover 

the  surface. 

Shelters  also  limpet-shaped — It  should  be  noted  in 
passing  that  this  flattened  form,  which  is  characteristic 
of  so  many  members  of  lotic  society,  is  characteristic 
not  only  of  the  living  animals  but  also  of  their  shelters. 
The  tarpaulin-like  web  of  the  moth  Elophila  fidicalis 
is  flat,  and  the  pupal  shelter  is  quite  limpet-shaped. 
The  case  of  Leptocerus  ancylus  is  widely  cornucopia- 
shaped,  its  mouth  fitted  to  the  stone.  The  coiled 
case  of  Helicopsyche  is  a  very  broad  spiral,  closely 


Fig.  223.     Larval  cases  of  the  midge,  Tanytarsus, 
attached  to  a  stone  in  running  water. 


Fig.  224.     The  maxilla  of  a  mayfly,  Amelctus  ludens, 
showing  diatom  rake. 


374 


Aquatic  Societies 


attached  in  the  hollows  of  stones  and  crevices  of  rock 
ledges.  The  case  of  the  caddis-worm,  Ithytrichia,  (fig. 
162  on  p.  2(12)  is  broadly  depressed. 

Thus  the  impress  of  environment  is  seen  not  only 
in  the  form  of  a  living  animal  but  also  in  that  of  the 
non-living  shelter  that  it  builds.  In  this  there  is  a 
parallel  of  form  in  the  secreted  shell  on  the  back  of  the 
snail,  Ancylus,  and  manufactured  shell  on  the  back  of 
the  caddis-worm,  Helicopsyche.  One  would  have  to 
search  widely  to  find  better  examples  of  the  effects  of 
environment  in  molding  to  a  common  form  these 
representatives  of  many  groups  of  very  diverse  struc- 
tural types.  Two  of  them,  at  least,  were  sufficiently 
like  lotic  mollusca  to  have  deceived  their  original 
describers.  Psephenus  was  first  described  as  a  limpet 
and  Helicopsyche  as  a  snail. 

Foraging  habits — The  food  of  the  herbivores  in  lotic 
societies  is  algae.     There  are  none  of  the  higher  plants 

present,    save    a   few 


r 


mosses  of  rather  local 
distribution.  It  is  not 
surprising  therefore 
that  the  food  gather- 
ing apparatus  of  these 
forms  should  present 
special  adaptative 
peculiarities.  The 
mouth-parts  of  may- 
flies and  of  midges 
show  much  develop- 
ment of  diatom  rakes 
and  scrapers.  For 
scraping  backward 
the  labrum  is  often 
used.  In  the  net-spinning  caddis-worms  it  is  bordered 
on  either  side  by  a  stiff  brush  of  bristles,  and  in  midge 


Fig.  225.  The  sheltering  tubes  of 
midge  larvae.  Photographed  under 
running  water  on  the  rocky  bed  of  a 
stream. 


Foraging  Habits 


o/o 


larvas  there  is  developed  both  before  and  behind  its 
border  a  considerable  array  of  combs  and  rakers.  In 
use  the  head  is  thrust  forward,  and  these  are  dragged 
backward  across  the  surface  that  supports  the  growth 
of  diatoms  and  other  algas. 

The  principal  carnivores  of  the  rapids  are  the  nymphs 
of  stoneflies  (see  fig.  in  on  p.  204)  and  a  few  small 
vertebrates.  Among  the  latter  are  the  insect-eating 
brook  salamander,  Spelerpes,  and  a  number  of  small 
fishes,  such  as  darters,  dace  and  minnows. 


CHAPTER   VII 

INLAND   WATER   CULTURE 


ABORIGINAL 
fflEK    CULTURE 


ARDLY  any  native 
species  found  by  the 
white  man  in  America 
had  done  so  much  to 
alter  and  improve  its 
environment  as  had  the 
American  beaver.  Cer- 
tainly the  red  man  had 
done  less.  Thousands 
of  acres  of  fertile  valley 
land  now  tilled  by  Amer- 
ican  plowmen  was 
levelled  up  behind 
beaver  dams.  These  followed  one  another  in  close 
succession  in  the  valley  of  many  a  woodland  stream. 
The  wash  from  the  hills  settled  in  their  basins.  As 
they  were  filled,  dams  were  built  higher,  and  thus  the 
rich  soil  grew  deeper. 

The  beaver  was  a  builder  of  ponds.  His  only  method 
was  by  damming  gentle  streams.  He  cut  down  trees 
with  his  great  chisel-like  teeth,  trees  often  six,  eight,  or 
ten  inches  in  diameter.     He  cut  off  their  boughs  and 


377 


378 


Inland  Water  Culture 


drew  them  to  the  place  where  a  dam  was  to  be  con- 
structed. He  piled  them  as  a  framework  for  a  dam, 
weighted  them  in  position  with  stones,  filled  the  inter- 
stices with  trash  and  leafage  and  covered  the  water 
side  over  completely  with  mud,  making  it  impervious. 
And  when  the  water  had  risen  behind  it  he  built  him  a 
dome-shaped  house  on  the  edge  of  the  pond  thus 
created,  having  passageways  opening  beneath  the 
water,  and  he  plastered  it  over  with  mud.  When 
marsh  plants  grew  about  the  edges  of  the  lands  he  had 
thus  inundated,  he  cut  channels  through  them  for  easy 
passage  to  his  favorite  feeding  grounds.  His  staple 
food  was  the  bark  of  aspens  and  birches  that  grew 
thickly  near  at  hand,  but  this  he  varied  with  succulent 
shoots  and  tubers  of  aquatics*  These  nature  planted 
for  him,  as  soon  as  he  had  prepared  his  water-garden. 
This  was  aboriginal  water  culture. 


Fig.  226.  An  aboriginal  water-garden.  A  beaver  dam  and  pond.  (From  Morgan.) 


ATER    CROPS 


ERTILITY  dwells  at  the 
water  side,  where  the 
essential  conditions  for 
growth — m  o  i  s  t  u  r  e  , 
warmth,  air  and  light — 
abound.  There  Nature's 
crops  are  never  failing. 
They  are  abundant  crops 
compared  with  which  the 
herbage  of  the  uplands 
appear  thin  and  scatter- 
ing .  If  they  are  not  our 
crops,  that  is  not  Nature's 
fault  but  our  own.  We 
have  given  all  our  toil  and  care  to  the  cultivation  of  the 
products  of  the  land,  and  have  left  the  waters  to  pro- 
duce what  they  might,  often  in  the  face  of  neglect  and 
injury. 

Time  was  when  the  waters  furnished  to  man  the  most 
dependable  part  of  his  livelihood — fish  and  oysters  and 
edible  roots  and  excellent  furs.  That  was  before  the 
days  of  agriculture.  Primitive  man,  while  gathering 
his  fruit  and  roots  and  grains  from  the  wild,  saw  the 
supply  failing  and  planted  a  garden  to  increase  his 
sustenance.  Had  he  by  like  means  endeavored  to 
supplement  his  stores  of  water  products,  we  might  now 
have  had  a  water  culture,  comparable  with  agriculture. 
A  number  of  native  water  plants  furnished  food  to 
the  red  men  in  America.     One  of  these,  the  wild  rice 


379 


38o 


Inland  Water  Culture 


1 

/ 

•. 

' 

i 

t 

-  'j. 

\j 

4 

; 

V 

t 

tt^hmf' 

'  1 

/£ 

fk    J 

'\%^£ 

**/\ 

Fig.  227.  A  flower-cluster  of  wild  rice,  fertile 
above,  staminate  below.  Little  brown  syrphus 
flies  of  the  genus  Platypeza  cling  to  the  stam- 
inate blossoms. 


(fig.  227),  is  ob- 
tainable in  our 
own  markets  in 
very  limited 
quantity  and  at 
fancy  prices :  it 
grows  as  a  wild 
plant  still.  The 
Indian  ate  both 
the  nut-like  seeds 
and  the  stocks  of 
the  wild  lotus ; 
also  the  tubers  of 
the  arrowhead, 
the  stocks  of  the 
arrow- arum,  the 
enormous  rhizo- 
mes of  the  spat- 
terdock,  the  suc- 
culent shoots  of 
the  cat-tail,  and 
other  rather 
coarse  and  watery 
wild  plant  pro- 
ducts, that  we 
esteem  better 
food  for  muskrats 
than  for  men. 
The  starch-filled 
tubers  of  the  sago 
pondweed  (fig. 
228)  are  choice 
food  for  water- 
fowl, and  if  ob- 
tainable in  suffi- 
cient quantity 
would     probably 


Water  Crops 


38i 


be  prized  by  men,  for  when  cooked  they  are  both  pleas- 
ing in  appearance  and  very  palatable. 

A  number  of  rushes  of  different  sorts  were  in  aborigi- 
nal times  used  for  coarse  weaving  of  mats,  etc.;  and 
one  of  these,  the  narrow-leaved  cat-tail,  we  have  of  late 
begun  to  use  in  new  ways;    in  paper  making  and  in 


Fig.  228.     Tubers  of  the  sago  pondweed. 
Potamogeton  pectinatus. 

cooperage.  The  initial  cut  on  the  preceding  page  shows 
a  field  of  cat-tail  carefully  cut  and  shocked  for  use  in  the 
calking  of  barrels  that  are  to  hold  watery  liquids.  The 
leaves  are  placed  singly  between  the  staves  of  the 
barrels,  where  they  swell  when  wet,  packing  the  joints 
tightly. 

It  may  be  that  none  of  these  plants  will  ever  be  cul- 
tivated.    Some  are  abundant  enough  for  present  needs 


382 


Inland  Water  Culture 


without  it.  Wild  rice  is  but  another  cereal  grain,  tho 
an  excellent  one.  We  already  have  garden  roots  in 
great  variety  of  sorts  that  we  prize  more  highly  than 
do  these  wild  aquatics.  The  white  water  lily  wTill 
be  cultivated  in  the  future  for  its  beautiful  flowers 
rather  than  for  its  edible  tubers. 


at 

A 

ft 

JS 

<*fM 

> 

HL 

■^  J^k 

WV 

Fig.  229.     The  white  water  lily,  Castalia  odorata. 


The  animal  produets  of  the  water  are  more  important. 
Aquatic  molluscs,  crustaceans,  and  vertebrates  have 
ever  furnished  staple  foods.  Tho  fresh  water  molluscs 
are  no  longer  eaten,  immense  accumulations  of  their 
shells  along  some  of  our  inland  waterways  bear  silent 
testimony  to  the  extent  to  wThich  they  were  once  con- 
sumed by  the  aborigines.  Their  shells  also  served 
other  primeval  uses,  as  cups  and  as  scrapers.  In  our 
own  day  a  new  and  important  use  has  been  found  for 
them  in  the  manufacture  of  pearl  buttons  and  orna- 


Fish 


383 


ments.  They  make  the  best  of  buttons,  neat  and  dura- 
ble and  beautiful,  a  great  improvement  over  the  butt*  >ns 
of  wood  and  metal  formerly  in  use.  The  annual 
product  of  pearl  buttons  from  this  source  is  now  worth 
many  millions  of  dollars.     It  is  all  derived  from  wild 


Fig.  230.    Valve  of  a  mussel  shell,  with  "blanks"  cut  from  it, 
in  process  of  manufacture  into  pearl  buttons. 

mussels;    the  method  in  use  is  exploitation,  not  hus- 
bandry. 

Fish — The  great  staple  food  product  of  the  water  is 
fish.  In  our  day  frogs  are  used  but  locally  and  fresh 
water  crustaceans  and  other  animals,  hardly  at  all; 
but  fishes  are  used  everywhere.  They  have  been  a 
staple  food  from  the  beginning  of  human  history,  and 
probably  will  be  to  the  end.     Hence  it  is  that  inland 


384  Inland  Water  Culture 


water  culture  means  to  a  large  extent  the  raiding  of 
fishes. 

Fish  culture*  in  America  is  in  a  very  backward  state 
as  compared  with  animal  husbandry  in  other  lines. 
This  is  manifest  in  many  ways;  among  them,  the 
following: 

1.  There  is  lack  of  improved  cultural  varieties. 
Our  fishes  are  wild  fishes.  Save  for  a  few  races  of  gold 
fishes  all  fancier's  fishes — and  some  not  very  desirable 
varieties  of  carp,  hardly  any  improvements  have  as 
yet  been  made  by  selection  and  careful  breeding. 

2.  There  is  lack  of  knowledge  of  the  best  kinds  of 
forage  for  fishes  and  of  how  it  may  be  provided  for  their 
use.     This  is  half  of  the  problem  of  raising  any  animal. 

3.  There  is  lack  of  any  practical  system  of  manage- 
ment, that  provides  for  the  breeding  and  feeding  and 
rearing  of  stock,  generation  after  generation,  under 
control. 

In  what,  then,  does  the  fish  culture  of  the  present 
consist?  Mainly  in  this  one  thing,  the  care  of  the 
young.  This  includes  the  gathering  and  hatching  of 
fish  eggs  and  the  rearing  of  the  young  fishes  thro  their 
earlier  stages  on  artificial  food  in  hatcheries.  By  this 
means  the  enormous  losses  that  occur  under  natural 
conditions  in  early  life  are  avoided,  and  vast  numbers 
of  fry  and  fingerlings  are  grown  to  a  size  suitable  for 
planting  in  natural  waters.  Thus  far  the  methods  are 
well  worked  out.  Thus  far  our  fish  culture  is  bril- 
liantly successful.  But  this  is  really  only  the  first  step. 
How  these  little  fishes  when  turned  loose  in  pond  and 
stream  shall  find  for  themselves  the  means  of  a  liveli- 
hood is  the  unsolved  part  of  the  problem.  Planted 
here  they  seem  to  thrive:     there,   they  fail.     Every 

The  substance  of  the  following  pages  covering  this  subject  was  published 
by  the  senior  author  in  the  Indianapolis  News  in  1909,  and  again  in  the  Farmers 
Magazine  in  19 12. 


Fish  Culture  38; 


planting  in  a  new  place  is  more  or  less  an  experiment. 
Sheep  culture  would  be  in  a  state  quite  comparahlc 
with  the  fish  culture  of  to-day,  if  after  rearing  lambs 
on  the  bottle  they  were  turned  loose  in  an  unexplored 
forest  to  shift  for  themselves. 

The  hatcheries  are  raising  fry  and  not  fishes.  This  is, 
of  course,  what  they  were  commissioned  to  do,  the 
underlying  idea  being  merely  that  of  putting  back  into 
the  lakes  and  streams  a  copious  supply  of  young  fishes 
to  occupy  the  place  of  the  adult  fishes  taken  out.  But 
experience  has  shown  that  the  mere  planting  of  fry 
soon  reaches  its  effective  limit,  after  which  the  planting 
of  more  fry  is  sheer  waste.  The  conditions  in  the  wild 
are  not  such  as  yield  much  advantage  from  this  intensive 
propagation  of  the  young.  Oftentimes  the  fry  planted 
in  the  trout  streams  about  Ithaca  may  be  found  shortly 
afterward  in  the  stomachs  of  the  few  adult  trout  that 
live  in  the  same  streams.  Feeding  fishes  on  the  young 
of  their  own  kind  is  not  good  husbandry. 

The  planting  of  fry  and  of  fingerlings  is  effective 
where  conditions  permit  of  their  growth.  The  rem*  >val 
of  enemies  is  a  supplemental  measure  of  great  value 
where  practicable.  The  care  of  natural  feeding  grounds 
to  prevent  their  destruction  is  very  important,  but 
usually  impossible,  for  want  of  enlightened  public 
opinion.  Protecting  of  breeding  fishes  when  on  their 
spawning  grounds — the  time  when  they  are  most 
easily  discovered  and  destroyed— is  also  very  impor- 
tant. And  the  bringing  back  into  habitable  places  of 
young  fishes  stranded  in  the  side  pools  of  bottomland 
streams,  where  they  would  perish  with  the  evaporate  »n 
of  the  water,  is  rescue  work  of  a  good  sort.  All  these 
things  are  done  in  the  interests  of  public  fishing  at  the 
present  day.  They  are  such  measures  as  are  taken  to 
preserve  wild  game  in  a  forest  or  livestock  on  an  open 
range.  They  have  to  do  rather  with  hunting  than  with 
husbandry. 


386  Inland  Water   Culture 

The  day  is  coming — is  already  at  hand — when  he 
who  wants  fishes  fresh  from  the  water  will  have  to 
raise  them.  Public  waters  are  "fished-out."  In  spite 
of  closed  seasons,  and  frequent  plantings  of  hatchery- 
reared  fry,  they  continue  to  be  "fished-out."  With  the 
growth  of  our  population  they  are  going  to  be  always 
' '  fished-out ; ' '  and  there  is  no  hope  for  the  future  of  any 
fishing  that  shall  be  worth  while  except  in  waters  that 
are  privately  controlled. 

Tins  does  not  mean  that  there  will  be  no  fishing  in 
the  future.  It  only  means  that  fish  raising  is  going 
the  way  wild  pig  raising  has  gone. 

When  game  began  to  fail — venison,  wild  turkeys,  etc. , 
the  pioneer  began  to  raise  pigs.  At  first  he  gave  them 
little  attention,  except  at  killing  time,  and  furnished 
them  no  food.  He  raised  them  about  as  we  raise 
fishes  now.  He  turned  them  loose  in  the  woods  to 
forage  for  themselves  as  we  now  plant  fish  fry  in  the 
streams.  They  ranged  the  whole  area  where  their 
food  grew. 

Nowadays,  thousands  of  hogs  are  raised  where  one 
was  raised  then,  but  they  do  not  run  the  range;  they 
are  kept  in  small  lots,  and  the  broad  areas  are  devoted 
to  raising  forage  for  them.  The  present  day  method 
of  obtaining  our  meat  supply  is  very  unromantic  as 
compared  with  chasing  a  razorback  hog  with  a  shot- 
gun through  the  woods  at  the  end  of  the  acorn  season, 
but  it  is  the  inevitable  way  of  progress  in  animal  hus- 
bandry. 

Raising  animals  and  their  forage  together  is  not  good 
husbandry.  It  is  exceedingly  wasteful  and  unproduc- 
tive; yet  that  is  the  way  we  still  raise  fish  in  America. 
We  ought  to  be  doing  better  than  this.  It  is  idle  to 
plant  more  fish  in  the  water  until  we  can  supply  more 
stuff  for  them  to  eat.  And  we  cannot  expect  more 
forage  to  grow  unless  we  provide  suitable  conditions. 


The  Forage  Problem  387 


When  we  raise  other  stock-feed  we  find  a  few  perfectly 

definite  things  to  be  done: 

1 .  We  clear  a  field  and  prepare  it. 

2.  We  fence  it  to  keep  out  enemies  and  undesirable 
competitors. 

3.  We  plant  it  with  selected  seed;  and  after  a 
period  of  growth, 

4.  We  use  the  crop  at  the  time  of  its  maximum 
value. 

All  these  things  we  shall  have  to  do  if  we  ever  have 
a  real  fish  culture.  The  first  two  of  these  things  arc 
usually  cared  for  in  the  construction  of  fish-ponds ;  the 
other  two  are  generally  neglected. 

The  forage  problem  is  less  simple  than  is  the  raising 
of  pigs  on  clover,  for  at  least  two  reasons: 

1.  Plant  foods  are  not  eaten  directly  by  the  more 
valuable  fishes,  and  often  there  are  a  number  of  turns- 
over  of  the  food  stuffs  before  the  fishes  are  reached. 
For  example,  diatoms  and  other  synthetic  plancton 
organisms  are  eaten  by  water-fleas  and  midge  larvae, 
that  are  in  turn  eaten  by  little  fishes,  that  are  eaten  by 
big  fishes.  There  must  be  at  least  two  turns-over — 
one  kind  each  of  plant  and  animal  forage — since  the 
desirable  food-fishes  are  carnivorous. 

2.  There  may  be  one  or  more  changes  of  diet  during 
development.  Thus  the  pike  when  newly  hatched  cats 
such  water-fleas  as  Simocephalus,  (see  fig.  92  on  p.  1  s<  >) 
picking  them  one  by  one  with  automatic  regularly- 
timed  snappings  of  its  jaws.  When  grown  a  little 
larger  it  eats  midge  larvae,  mayfly  nymphs  and  other 
small  insects.  Still  later,  it  eats  large  insects  and 
mixes  small  fishes  in  its  diet;  and  as  it  attains  full 
stature  it  restricts  its  diet  to  frogs  and  larger  fishes. 
When  grown  it  takes  hardly  anything  smaller  than  a 
golden  shiner. 


388  In  hind  Water  Culture 

Studies  of  the  food  of  the  common  sunfish,  Eupomotis 
gibbosus,by  the  senior  author  ('08)  have  shown  that  in 
Old  Forge  Pond,  when  one  inch  in  length  the  food  is 
predominantly  entomostraca  and  very  small  midge 
e.  When  two  inches  in  length,  it  is  entomostraca 
and  midge  larvae  of  larger  size,  together  with  small  may- 
fly nymphs  (Csenis)  and  minute  snails.  When  three 
inches  in  length,  it  is  gr<  >wn  midge  larvae,  mayfly  nymphs 
and  caddis- worms.     At  this  size  apparently  the  diet  of 


Fig.  231.     The  common  sunfish.     Eupomotis  gibbosus. 
(Photo  by  George  C.  Embody) 

entomostraca  and  small  midge  larvae  is  out  gown,  and 
the  fishes  are  seeking  bigger  game. 

At  three  inches  in  length,  this  fish  is  itself  the 
favorite  food  of  adult  bullheads. 

Excepting  for  a  few  fishes  that  range  the  open  waters, 
such  as  white-fish  and  lake  herring,  and  that  continue 
to  feed  largely  on  plancton,  there  is  at  least  one  neces- 
sary shift  of  diet  accompanying  growth;  that  from 
plancton  to  the  food  of  the  adult.  In  an  earlier  chapter 
(see  p.  235)  we  have  briefly  indicated  the  principal 
changes  of  diet  then  occurring. 


Staple  Foods 


389 


The  food  relations  of  aquatic  organisms  are  exceed- 
ingly complex.  They  change  with  age  and  season  and 
situation.  The  eater  and  the  thing  eaten  often 
exchange  roles.  Yet  there  are  some  fairly  constant 
food  dependencies  between  the  major  groups  of 
organisms.  These  have  been  set  forth  by  that  veteran 
student  of  the  forage  problem,  Prof.  S.  A.  Forbes,  in  the 
table  copied  herewith  (fig.  233),  and  this  table  indi- 
cates (what  detailed  food  studies  at  large  abundantly 
confirm)  that  fishes  eat  almost  every  living  thing  that 
the  water  offers. 


232.     The  nymph   of   the   dragonfly,    A 
Junius,  devouring  a  small  sunfish. 


Fig 


nax 


The  young  of  all  fishes  eat  plancton.  This  sounds 
like  one  point  of  general  agreement,  until  we  reflect 
on  the  variety  of  organisms  of  which  plancton  is  com- 
posed. Which  of  these  are  best  for  use  in  fish  culture 
we  scarcely  know  at  all.  Fortunately,  they  are  of 
nearly  universal  distribution  in  shoal  fresh  waters, 
where  the  young  of  fishes  are  found. 

Staple  foods — While  a  list  of  all  foods,  eaten  by  all 
fishes  would  include  practically  every  thing  that  is 
found  in  the  water,  yet  when  careful  food  studies  are 
made  there  are  a  number  of  organisms  so  constantly 
recurring  that  they  stand  out  as  of  prime  importance. 
A  few  aquatic  herbivores  are  found  as  commonly  and 


390 


Inland  Water  Culture 


as  regularly  in  the  stomachs  of  wild  food  fishes,  as  grass 
would  be  found  in  the  stomachs  of  wild  cattle.  And 
just  as  stock  feeding  has  made  progress  with  the  isola- 
tion and  study  and  increase  of  the  grasses,  so  fish  cul- 
ture would  be  advanced  by  study  and  cultivation  of 
the  staples  of  wild  fish  food. 


PRINCIPAL 

FOOD  RELATIONS 

or 
AQUATIC    ORGANISMS 

(ILLINOIS) 

5 

<«1 
o 

J; 
(a 

N 

o 

Q 

1 

<-> 

III 
*■> 

*> 
k 

S! 

5 

III 

hi 

5 

III 

K 

k 

<-> 

Q 

^ 

T 

^ 

Terrestrial  Wastes 

X 

X 

X 

X 

-• 

• 

X 

X 

X 

X 

X 

X 

Bactc pia 

X 

X 

X 

X 

X 

X 

X 

Algal 

X 

X 

X 

X 

X 

X 

X 

X 

Hicher  Plants 

X 

X 

X 

X 

X 

Protozoa 

X 

X 

x 

X 

X 

> 

Rotifers 

X 

x 

X 

X 

Pntomostraca 

X 

X 

X 

X 

X 

X 

X 

Worms 

X 

X 

X 

X 

Cra  w pishes 

X 

X 

X 

X 

X 

INSECTS 

X 

X 

X 

x 

X 

• 

X 

AAOLLUSKS 

> 

X 

X 

X 

,' 

Pishes 

X 

:>- 

X 

X 

X 

X 

X 

X 

X 

X 

PROCS 

X 

X 

X 

X 

X 

X 

Turtles 

X 

X 

Serpents 

X 

Birds 

X 

X 

Fig.  233.     Forbes'  (14)  table  of  food  (at  left)  and  feeding 
organisms  (above). 


Our  best  fishes  are  carnivores,  and  the  animals  they 
eat  are  chiefly  a  few  hardy,  prolific,  and  widely  dis- 
tributed herbivores,  such  as  water-fleas,  scuds,  midge 
larvae,  mayfly  nymphs  and  other  fishes.  These  feed, 
of  course,  on  plants;  but  we  hardly  know  as  yet  what 
plants  are  of  most  value  to  them.  They  thrive  where 
herbage  abounds ;   and  yet  we  know  that  abundance  of 


Water- Fleas 


39 1 


herbage  may  not  necessarily  mean  good  crops;  for 
weeds  may  be  much  more  conspicuous  in  a  pasture  than 
the  close-cropped  grasses  that  yield  the  forage  there. 
Certain  species  of  pond  weeds  have  been  shown  by 
Miss  Moore  ('15)  to  be  often  used  as  green  food,  and 
Birge  ('11)  has  given  many  notes  on  the  food  preferences 
of  herbivorous  plancton  Crustacea. 

The  above  mentioned  staples  invite  much  attention 
but  we  shall  have  space  for  noticing  but  a  few  represen- 
tatives of  the  groups  to  which  they  severally  belong. 


Digestive    tract 
Abdominal    processes 


Brood' chamber 
Heart 


Abdominal  cfaws' 

Post- abdomen 


Fig.  234.     Daphne  (after  Dodds). 

Water-fleas — As  a  typical  representative  of  this  great 
group  of  herbivores,  we  may  speak  of  Daphne  (fig.  234). 
Its  manner  of  life  and  its  enormous  reproductive 
capacity  have  already  been  briefly  mentioned  (pp.  186-7 
and  306) .  It  is  a  very  valuable  animal  in  water  cult  tire 
on  account  of  its  ability  to  turn  the  great  growths  of 
colonial  diatoms  and  algas  into  excellent  food  for  fishes. 
Little  is  known,  as  yet,  unfortunately,  about  the  condi- 
tions that  make  for  its  growth.     Plancton  studies  of 


392  Inland  Water  Culture 


water-fleas  have  consisted  in  the  main  of  the  counting 
of  individuals  in  random  catches;  and,  as  Hasckel  ('90) 
long  ago  pointed  out,  this  has  about  as  much  economic 
value  as  the  counting  of  straws  would  have  in  an  oat 
field. 

The  extraordinary  growths  of  certain  plancton  algae 
(Anabaena,  Aphanizomenon,  etc.)  that  often  give 
trouble  in  water-supply  reservoirs,  might  be  made  into 
fish  food  through  the  agency  of  daphnias,  if  we  only 
had  learned  how  to  manage  our  water  crops. 


Fig.  235.     Gammarus  fasciatus  (after  Paulmier). 

Water-fleas  are  of  very  great  value  as  food  for  young 
fishes,  they  form  also  a  considerable  part  of  the  food 
of  such  larger  fishes  as  are  equipped  with  gill  strainers 
for  gathering  them  out  of  the  waxer.  They  are,  of 
course,  largely  absent  from  the  water  during  the  winter 
season.  Their  value  as  forage  organisms  lies  in  their 
good  quality  and  their  extraordinary  reproductive 
capacity. 

The  sctcds — This  group  of  herbivores  is  typified  by 
Gammarus  (fig.  235)  a  hardy,  wide-ranging  habitant  of 
the  water  weeds.  It  swims  well,  yet  prefers  to  occupy 
the  sheltering  crevices  of  dense  leafage.     It  can  leap 


The  Scuds  303 


and  dodge  like  a  rabbit.  It  feeds  on  a  great  variety  of 
both  living  and  dead  herbage.  It  is  itself  a  favorite 
food  for  most  fishes.* 

The  scuds  are  easily  managed  in  pond  culture.  They 
are  not  remarkably  prolific.  As  already  mentioned  on 
page  190,  the  possible  progency  of  a  single  pair  in  one 
year  is  somewhat  less  than  25,000.  But  they  carry 
theiryoungin  a  pectoral  brood  pouch  until  well  equipped 
for  life. 

The  chief  merits  of  the  scuds  as  forage  organisms 
(in  addition  to  desirability  as  food)  lie  in  their  hardi- 
ness, their  ability  to  find  a  living  and  to  take  care  of 
their  own  young  until  well  started  in  life,  their  constant 
succession  of  overlapping  broods  thro  the  season  and 
their  permanent  residence  in  the  water. 

There  are  other  herbivorous  crustaceans  of  some- 
what similar  habits,  among  which  the  fresh-water 
prawn,  Palasmonetes,  is  probably  useful  as  fish  forage. 

Midge  larvce — Larvae  of  midges  of  the  genus  Chirono- 
m us  popularly  known  as  "blood-worms"  (fig.  236)  are 


Fig.  236.     A  "blood- worm." 


of  prime  importance  as  fish  food.     Small  ones  are  ei 
almost  as  universally  as  are  plancton  entomostraca, 
and  the  large  ones  continue  to  be  eaten  whenever 
obtainable  by  fishes  as  large  as  adult  trout  and  white- 


*Its  value  has  long  been  recognized  by  fishermen;  on  account  of  its  abund- 
ance in  an  excellent  trout  stream  at  Caledonia,  N.  Y.,  it  has  1  »een  locally  known 
as  the  "Caledonia  shrimp." 


394  Inland  Water  Culture 

fish.  In  a  most  extensive  examination  of  the  contents 
( >f  fish  stomachs  Forbes  ('88)  found  them  "of  remarkable 
importance,  making  in  fact  nearly  one-tenth  of  the 
f<  .<  >d  of  all  the  fishes  studied."  Ferguson  fed  some  red- 
bellied  minnows  (Chrosomus  erythrogaster)  for  22  days 
all  the  midge  larvae  (Chronomus  viridicollis)  they  would 
eat  and  nothing  else.  The  grown  minnows  ate  on  an 
average  twenty-five  blood-worms  per  day;  the  half- 
gr<  >\vn  ones,  eleven.  The  senior  author  ('03)  found  that 
25  brook  trout  taken  at  random  from  one  of  the  best 
natural  ponds  of  the  New  York  State  Fish  and  Game 
Commission  at  Saranac  Inn,  N.  Y.,  had  in  their 
stomachs  more  than  100  blood-worms  each. 

Midge  larvae  are  among  the  most  ubiquitous  of 
freshwater  organisms.  They  feed  mainly  upon  dia- 
toms, and  other  simple  organisms  found  in  water  or 
growing  sessile  on  or  round  about  their  homes;  the 
larger  ones  eat  also  the  disintegrating  tissues  of  the 
higher  plants.  They  dwell  among  all  sorts  of  aquatic 
plants,  spreading  their  thin  filmy  tubes  in  every  crevice 
or  along  the  stems.  Little  is  seen  of  them  there  on 
casual  observation.  They  are  like  the  rodents  of  the 
fields,  hidden  in  their  runways.  But  one  cannot  place 
a  handful  of  any  water  weed  in  a  dish  of  water  without 
soon  seeing  some  dislodged  midge  larvae  swimming 
about  the  edges  with  characteristic  figure-of-8-shaped 
loopings  of  the  body. 

They  dwell  on  the  bottom  (see  fig.  134  on  p.  226). 
Indeed,  as  already  noted,  they  may  dwell  far  out  on  the 
bottom  under  the  deep  water  of  great  lakes.  Here  in 
deep  darkness  and  heavy  pressure  they  dwTell  in  enor- 
mous numbers  feeding  upon  the  rich  spoils  of  the  plancton 
rained  down  on  them  by  gravity  from  above.  They 
often  fill  the  soft  bed  with  their  silt-covered  flocculent 
tubes. 


Midge  Larvce  395 


These  tubes,  like  the  ones  on  the  stems,  open  to  the 
surface  at  both  ends.  The  larva,  within,  holding  on  t<  1 
the  silken  lining  of  the  walls  with  its  claws,  swings  its 
body  in  vigorous  undulations,  driving  a  current  of 
water  thro  the  tube.  This  serves  for  respiration.  It 
also  serves  to  drive  diatoms  and  other  food  organisms 
into  net-like  barriers  spun  across  the  exit;  these  bar- 
riers are  repaired  or  renewed  after  every  catch.  Food 
is  thus  carried  into  the  shelter  of  the  case.  But  food 
is  also  gathered  from  exposed  surfaces  whenever  it  can 
be  reached  from  open  ends  of  the  tube.  It  is  gathered 
by  scraping  the  sessile  diatoms  and  algae  from  stems. 
For  such  work  the  mouth  of  the  larva  is  equipped  with 
elaborate  rakes  and  scrapers. 

The  larva  of  Chironomus  is  relatively  simple.  It 
appears  much  less  complex  in  organization  than  are 
many  of  its  insect  competitors.  It  has  a  cylindric 
worm-like  pale  and  naked  body  with  a  bifid  proleg 
underneath  at  the  front  and  a  pair  of  prolegs  behind, 
caudal  tufts  of  bristles,  and  a  few  simple  gills.  The 
prolegs  are  armed  with  hooks  and  on  them  it  creeps 
somewhat  like  a  looping  caterpillar.  From  its  mouth 
it  spins  the  fluid  silk,  and  spreads  it  ere  it  hardens  with 
the  front  proleg.  All  in  all,  it  is  a  shy  and  defenseless 
and  secretive  creature,  without  any  special  gift  of 
locomotion. 

This  apparent  weakling  has  been  able  to  possess 
itself  of  the  entire  littoral  region  of  the  earth,  perhaps 
by  reason  of  the  following  characteristics : 

1.  Ability  to  live  on  foodstuffs  that  have  a  very 
general  distribution. 

2.  Ability  to  build  its  own  shelter. 

3.  Consequent  adaptability  to  variety  of  conditi<  ms. 

4.  Great  reproductive  capacity. 

5.  Brief  life  cycle. 


396 


I)i land  Water  Culture 


Chironomus  lays  several  hundred  eggs,  and  in  the 
warm  season  a  generation  may  completely  develop  in 
five  or  six  weeks;  so  the  very  considerable  increase  of 
one  brood  may  be  rapidly  repeated  in  geometric  ratio. 

The  limitations  to  its  use  as  a  forage  organism  in  fish 
ponds  lie  in  its  complicated  life  history.  It  quits  the 
water  at  the  end  of  the  pupal  stage.  It  flies  away, 
mates  in  the  air,  and  returns  to  the  water  to  lay  its  eggs. 
During  its  aerial  life  it  is  not  easily  managed. 

Mayfly  nymphs  constitute  one  of  the  most  important 
groups  of  aquatic  herbivores.  We  single  out  Callibsetis 
for  illustration  of  another  staple  fish  food.  It  is  an 
active  nymph  that  swims  from  place  to  place  by  means 


. J^ 


^p — ?  /     ' 


Fig.  237.    The  nymph  of  Callibaetis:     Drawing  by  Anna  H.  Morgan. 
(From  Annals  Ent.  Soc.  America) 


Callibcetis 


397 


of  quick  strokes  of  its  tail  and  gills,  and  that  clambers 
freely  about  over  shore  vegetation.  It  is  an  artful 
dodger;  and  it  is  protectively  colored.  It  feeds  on  a 
great  variety  of  vegetable  substances  living  and  dead, 
and  hence  finds  abundant  food  in  every  weedy  pond. 
It  is  eaten  by  every  carnivore  in  the  pond  that  can 
catch  it ;  and  doubtless  it  has  many  enemies  that  exceed 
it  in  swiftness  and  many  others  that  lie  in  ambush  and 
capture  it  by  stealth.  Hence,  tho  nearly  always 
present,  it  rarely  appears  very  abundantly  in  old 
ponds. 

The  life  cycle  of  Callibaetis  is  run  in  less  than  six 
weeks.  A  single  female  may  lay  iooo  eggs.  If  all 
these  were  to  develop  and  reproduce,  the  increase  from 
a  single  pair  during  one  summer  season  would  be  some- 
thing like  this: 

ist  brood  1,000  (half  females) 

2d  brood  500,000. 

3d  brood  250,000,000. 

4th  brood  125,000,000,000. 

These  alluring  possibilities  of  increase  in  an  organism 
that  is  choice  fish  food  once  led  the  senior  author  into  a 
series  of  experiments  that  extended  through  two  years 
and  that  met  with  uniform  failure  because  the  breeding 
of  the  mayflies  could  not  be  controlled.  The  rearing 
was  easily  managed  but  even  with  the  largest  measure 
of  freedom  that  could  be  provided,  the  adults  would 
not  mate  and  lay  eggs  in  captivity.  The  problem  of 
their  successful  artificial  propagation  is  still  unsolved. 
However,  there  has  never  been  a  new  pond  opened  at 
the  Cornell  University  Biological  field  station,  that  has 
not  received  the  eggs  of  wild  females  of  Callibaetis,  and 
that  has  not  raised  a  good  crop  of  the  nymph! 
their  slower-breeding  carnivorous  enemies  developed. 


398  Inland  Water  Culture 

Mayflies,  like  Callibsetis  and  the  little  Caenis,  that 
have  a  number  of  broods  each  season  with  overlap  of 
generations,  are  suited  for  use  in  forage  propagation 
because  at  all  times  of  the  year  nymphs  of  good  size  are 
present  in  the  water.  On  the  other  hand,  such  forms  as 
Blasturus  cupidus,  which  flies  in  May,  and  Siphloniirus 
alter nat us  which  flies  in  June,  are  absent  from  the  water 
at  the  close  of  their  breeding  season  or  are  represented 
there  only  by  eggs  and  very  minute  nymphs. 

Best  known  of  the  mayflies  that  fishes  eat  are  the 
nymphs  of  the  big  burrowing  Hexagenias  from  lake 
and  river  beds.  Food  examinations  have  abundantly 
shown  their  importance.  However,  they  develop 
slowly,  requiring  at  least  two  years  to  reach  maturity. 

The  Hexagenia  nymphs  are  natural  associates  of 
bloodworms  on  the  lake  bottom.  They,  and  the  blood- 
worms with  them,  and  the  entomostraca  swimming 
above  them  are  the  mainstay  and  dependence  of  the 
lake's  fish  population. 

Other  herbivorous  insects  of  promise  as  forage  organ- 
isms are  caddis- worms  and  aquatic  caterpillars.  Other 
invertebrates  are  a  number  of  pond  snails.  But  the 
animals  above  discussed  we  regard  as  most  important. 

Forage  fishes — The  largest  single  item  in  the  bill-of- 
fare  of  fishes  generally  is  other  smaller  fishes.     Herbi- 


r^ 


Fig.  238.     The  golden  shiner. 

(Photo  by  George  C.  Embody) 


The  Way  of  Economic  Progress  399 

vorous  fishes,  non-competitors  for  food,  may  therefore 
be  used  to  furnish  a  principal  crop  of  animal  forage. 
For  this  use  carp  are  objectionable  because  they  grow 
too  fast  and  soon  become  too  large  to  be  swallowed  by 
the  other  fishes.  They  eat  the  eggs  of  bass,  and  root 
up  the  bottom  and  tend  to  exterminate  their  own 
vegetable  forage.  Minnows  are  also  objectionable 
because  they  eat  the  eggs  of  other  fishes.  But  very 
valuable  for  such  use  are  the  golden  shiner  (fig.  238), 
and  the  gizzard  shad,  (Dorosoma  cepedianum) ,  of  our 
great  rivers.  Even  the  goldfish  is  an  excellent  agent 
for  turning  masses  of  blanket  algae  and  other  soft  fresh 
vegetable  foods  into  excellent  forage  for  larger  fishes. 

The  way  of  economic  progress — The  future  of  fish 
culture  lies  in  further  scientific  studies  to  be  made 
along  the  lines  that  have  proven  of  value  in  the 
raising  of  land  animals.  More  knowledge  is  what  is 
needed : 

1.  Intimate  detailed  knowledge  of  the  fishes  them- 
selves is  needed;  knowledge  of  their  natural  history, 
their  requirements  of  food  and  of  protection  for 
their  young;  their  enemies,  internal  and  external; 
their  natural  races  and  possibilities  of  improvement  by 
breeding.  Only  such  knowledge  can  furnish  a 
basis  for  developing  methods  of  control. 

2.  Equally  detailed  knowledge  is  needed  of  the 
economic  species  that  furnish  forage  or  that  menace 
the  welfare  of  the  cultivated  species ;  knowledge  of  all 
the  more  important  ones,  from  the  forage  fishes,  crusta- 
ceans, insects,  snails,  etc.,  even  down  to  the  diatoms. 
The  product  must  be  followed  to  its  principal  sources 
and  the  cultural  relations  that  all  these  organisms  bear 
to  each  other  must  be  better  understood.  The  enemies 
of  every  stage  of  fish  life  must  be  studied  (fig.  239). 


400 


Inland  Water  Culture 


3.  More  knowledge 
is  needed  of  the  water 
bodies  themselves; 
knowledge  of  their 
physical,  chemical  and 
hydrographic  c  o  n  d  i  - 
tions,  their  purity,  con- 
tamination, and  all 
other  conditions  that 
affect  the  welfare,  that 
promote  or  hinder  the 
normal  growth  and  ac- 
tivities of  the  useful 
organisms  contained  in 
them.  We  must  know 
these  things  in  order 
to  know  how  to  make 
and  keep  the  waters  productive. 

Knowledge  is  being  accumulated  in  all  these  lines 
in  a  slow  and  desultory  way,  thro  the  voluntary 
activity  of  many  diverse  and  widely  scattered  agencies. 
Fish  culture  has  not  yet  had  the  benefit  of  that 
efficient  agency  of  economic  progress  that  has  brought 
such  rapid  improvement  in  animal  husbandry — the 
experiment  station.  A  fish  cultural  experiment  station 
is  what  is  now  urgently  needed :  an  institution  equipped 
for  water  culture,  and  charged  with  the  duty  of  carrying 
out  a  well  planned  line  of  experiments  bearing  on  its 
economic  problems.  This  is  needed  to  supplement  the 
hatcheries  and  to  bring  their  work  to  fruition. 


Fig.  239.  Eggs  of  the  pike,  Esox 
Indus,  overgrown  with  two  species  of 
fungus. 


WATER  CULTURE  AND  CIVIC 
IMPROVEMENT 


HE  three  chief  interests 
of  the  public  in  water 
culture  He  (i)  in  mak- 
ing the  waters  produc- 
tive ;  (2)  in  keeping  the 
waters  clean  and  (3)  in 
preserving  the  beauty 
of  the  waterside.  Hap- 
pily, these  are  con- 
cordant, and  not  con- 
flicting interests. 

Another  interest  of  everybody  is  in  pure  water  to 
drink.  For  city-dwellers,  public  water  supplies  must 
be  kept  uncontaminated — a  matter  of  ever  increasing 
difficulty  as  our  population  grows.  This  vast  subject 
falls  without  our  present  scope:  its  literature  may  be 
found  by  following  up  a  few  references  (Whipple,  et.  a  I.) 
given  in  the  bibliography  at  the  close  of  this  volume. 

There  are  two  very  large  reclamation  enterprises, 
with  which  water  culture  should  have  much  to  do  in  the 
future : 

1.  The  reclamation  of  waste  wet  lands,  and 

2.  The  utilization  of  water  reservoirs. 

A  few  words  may  be  said  here  concerning  each  of  th 


401 


402  Inland  Water  Culture 

WHAT   SHALL    BE    DONE   WITH   THK    MARSHES? 

There  are  millions  of  acres  of  waste  wet  lands  in 
America,  that  are  producing  little  or  nothing  of  value. 
That  this  land  will  yet  be  made  to  contribute  much 
more  largely  to  human  sustenance,  there  can  be  no 
doubt:  for, 

i .  It  is  the  richest  of  all  the  land,  in  foodstuffs  that 
make  for  soil  fertility.  It  contains  organic  remains 
accumulated  for  ages,  together  with  the  wash  from 
surrounding  slopes. 

2.  It  is  generally  the  best  located  of  all  the  land 
with  respect  to  transportation  facilities.  Inland 
marshes  almost  everywhere  are  traversed  by  railways, 
their  levels  having  invited  the  attention  of  the  route- 
locating  engineer;  many  marshes  border  on  navigable 
waterways. 

3.  It  is  the  last  of  the  land  available  for  occupation, 
and  with  our  population  quadrupling  every  century, 
the  pressure  for  room  is  becoming  ever  more  intense. 

While  it  is  inevitable  that  most  of  this  land  will  yet 
be  used  for  production  of  human  food,  it  is  by  no  means 
certain  how  this  may  best  be  done.  Drainage  is  the 
one  method  hitherto  tried,  but  drainage  has  its  serious 
limitations : 

1.  Much  of  the  wet  land  cannot  be  profitably 
drained. 

2.  Its  value  as  a  water  reservoir  is  largely  destroyed 
by  drainage. 

There  is  another  plan  for  making  marshes  productive 
that  has  not  yet  been  tried  on  any  adequate  scale — a 
plan  that  involves  water  culture  as  well  as  agriculture. 
The  marshes — now  neither  wet  nor  dry — cannot  be 
used  as  they  are;  but  if  by  a  shifting  of  some  of  their 
topsoil  they  be  made  in  part  into  permanently  dry, 
and  in  part  into  deeper  reservoirs  of  water,  they  might 


The  Wastage  of  Reservoir  Sites  403 

then  be  cultivated  in  their  entirety.  The  dry  part 
would  be  available  for  ordinary  agricultural  use  and 
crops  can  be  grown  by  methods  already  well  worked 
out.  The  permanent  water  could  be  made  to  produce 
fish  and  fish  forage  and  other  water  crops.  The 
advantages  of  this  plan  over  drainage  would  appear 
to  be  the  following: 

1.  Increased  productiveness. 

2.  Permanent  water  storage. 

3.  Diversifying  of  crops:  it  would  not  be  merely 
adding  more  of  crops  already  extensively  cultivated. 

4.  Diversifying  the  industries  of  the  people. 

5.  Completer  utilization  of  the  wet  areas. 

THE   WASTAGE   OF  RESERVOIR  SITES 

There  is  another  service  that  water  culture  may 
render  to  great  public  works.  It  may  make  water 
reservoirs  productive.  The  various  measures  now 
being  widely  considered  for  the  development  of  our 
water  resources  should  be  co-operative  rather  than  con- 
flicting. The  making  of  reservoirs  for  holding  the 
surplus  rainfall  near  the  headwaters  of  streams,  allow- 
ing it  to  flow  as  needed,  should  result  in  three  distinct 
and  permanent  civic  benefits: 

1.  Permanent  water  power. 

2.  Continuous  navigation. 

3.  Increased  production  of  food. 

One  of  the  things  that  has  stood  in  the  way  of  the 
development  of  reservoirs  has  been  the  necessity  for 
condemnation  of  valuable  agricultural  lands  needed 
for  the  reservoir  site.  Such  lands  when  covered  with 
water,  are  of  course,  removed  from  agricultural  use. 
But  they  might  yet  be  used  for  water  culture,  and 
indeed  the  value  of  the  resulting  crops  might  thereby 
be  increased. 


404  Inland  Water  Cult  it 


re 


Some  special  development  of  the  water  bed  would, 
of  course,  be  needed  to  fit  them  for  an  intensive  water 
culture.  The  one  great  open  basin  of  water,  now  full 
and  now  reduced,  that  is  the  usual  thing  in  reservoirs, 
would  hardly  suffice.  But  with  no  extraordinary- 
increase  of  cost  the  greater  part  of  the  bottom,  espe- 
cially in  shoal  water,  might  be  divided  into  fish  ponds, 
so  constructed  as  to  be  under  control.  By  deepening 
these  considerably  and  using  the  excavated  earth  for 
building  strips  of  dry  land  between  them,  the  holding 
capacity  of  the  reservoir  might  be  increased.  It  would 
be  increased  by  just  so  much  as  the  volume  of  earth 
taken  from  below  and  placed  above  the  high  water 
level.  Then  as  much  water  as  under  the  present  plan 
could  be  drawn  off  for  power  or  navigation,  and  the 
residue  in  the  pond  bottom  would  suffice  for  main- 
tenance of  the  fishes  therein. 

On  this  plan,  in  a  reservoir  of  100  acres  having  90 
acres  of  shoal  water  on  which  fish  ponds  could  be 
developed,  50  acres  could  be  permanently  devoted  to 
fish  raising,  and  at  least  half  or  much  more  to  agricul- 
tural crops,  without  interfering  with  its  efficiency  for 
water  storage  and  regulation  of  stream-flow.  This 
would  be  much  better  than  having  it  all  lie  fallow  to  the 
end  of  time.  It  would  transform  a  water  waste  into  a 
water  garden.  Incidentally,  it  would  cure  also  the 
unsightliness  of  a  vast  area  of  exposed  and  reeking  mud 
during  the  season  of  low  water. 

The  beauty  of  the  shore-line — Another  public  interest 
with  which  water  culture  must  ever  be  identified  is  that 
of  preserving  the  beauty  of  the  landscape.  As  nature 
has  given  of  her  bounty  to  the  waterside,  so  also  she  has 
lavished  her  beauty  there. 

What  flowers  adorn  the  shore-line !  The  fragrant 
water  lily,  the  stately  lotus,  the  queenly  iris,  the  bril- 


The  Beauty  of  the  Shore  Line 


405 


liant  hibiscus,  the  soft  blue  pickerel -weed,  the  sweet 
forget-me-not!     What  foliage  in  pondweed  and  water 


Fig.  240.     The  common  wild  forget-me-no1 . 

shamrock,  in  arrowhead  and  arrow-arum,  in  water- 
shield  and  spatterdock!  What  exquisite  submerged 
meadows  the  pondweeds,  bladderworts  and  the  mil- 
foils make!     How  inviting  are  the  shores  where  these 


406  Inland  Water  Culture 


abound,  how  unattractive,  those  from  which  these  have 
been  removed. 

The  landscape  belongs  to  all.  Its  condition  affects 
the  public  weal.  It  is  good  to  dwell  in  a  place  where 
the  environment  breeds  contentment;  where  peace  and 
plenty  and  satisfaction  grow  out  of  the  right  use  of 
nature's  resources;  where  wise  measures  are  taken  to 
preserve  the  bounteous  gifts  of  nature  and  to  leave  them 
unimpaired  for  the  use  and  benefit  of  coming  genera- 
tions. 

Much  of  the  scenic  beauty  of  every  land  lies  in  its 
shore  lines;  and  it  should  be  a  part  of  public  policy  to 
keep  unimpaired  as  far  as  possible  the  attractiveness  of 
all  public  waters.  Streams  differ  far  less  from  one 
another  in  their  own  intrinsic  characters  than  in  the 
way  they  have  been  used  by  the  hand  of  man.  They 
differ  less  by  topography  and  latitude;  far  more  by  the 
cleanness  of  their  waters,  by  the  trees  that  crown  their 
headlands,  and  by  the  flower-decked  water-meadows 
that  fill  their  bays  and  shoals.  The  famous  distant 
lakes  and  streams  that  attract  so  many  people  far  from 
home  every  summer  are  not  more  beautiful  or  restful 
than  many  homeland  waters  once  were,  or  might 
again  be,  were  but  a  little  public  care  exercised  to  keep 
their  waters  clean  and  the  beauty  of  their  shores  and 
bordering  vegetation  unspoiled. 

Private  water  culture — Great  as  are  the  benefits  to  be 
hoped  for  in  public  works,  those  to  be  derived  from  the 
application  of  a  rational  water  culture  to  private 
grounds  are  probably  in  the  aggregate  far  greater.  On 
thousands  of  farms  there  are  waterside  waste  lands, 
lying  bare  and  abused,  that  might  be  reclaimed  to  use- 
fulness and  beauty  through  intelligent  water  culture. 

The  making  of  a  pond  on  the  home  farm  is  good  work 
for  the  slack  season;  and  once  properly  constructed  it 


Private  Water  Cult  lire 


4o; 


is  permanent,  and  will  with  a  minimum  of  attention 
yield  returns  out  of  all  proportion  to  its  cost.  It  will 
yield  fresh  fish  for  the  table.  It  will  yield  healthful 
sports  for  the  boys  and  girls  who  should  be  kept  at 
home;  angling,  and  swimming  in  the  summer  and 
skating  in  the  winter.  It  will  yield  beauty ;  the  beauty 
of  a  mirroring  surface,  reflecting  trees  and  hills  and 


Fig.  241 .     A  beautiful  cover  for  a  mud  bank, 
in  front,  then  arrowheads,  then  sedges. 


The  water-shamrock,  Marsilea, 


sky  and  passing  cloud;  the  beauty  of  the  aquatics 
planted  on  the  shore  line:  the  beauty  of  the  water 
animals,  of  flashing  dragonfly  and  gyrating  beetles,  and 
leaping  fishes.     It  will  add  to  the  joy  of  living. 

The  accompanying  diagram  is  intended  as  a  sugges- 
tion for  the  development  of  a  tract  of  upland  waste  wet 
land  into  a  water  garden.  Its  noteworthy  features  arc 
found  in  the  provision  for  growing  forage  under  control, 
and,   in  so  far  as  need  be,   apart  from  the   animal- 


408 


Inland  Water  C  allure 


Fig.  242.     Diagram  illustrating  the  conditions  for  fish  production  on  an  80 

acre  tract  of  wet  upland,  traversed  by  a  trout  stream.     A,  in  a  wild  state. 

B,  equipped  for  intensive  fish  raising. 
Area  devoted  to  fish,  in  A,  one  acre  more  or  less;  in  B,  one  acre  of  enclosed  ponds. 
Devoted  to  fish  forage,  in  A  the    same   acre    of   open    stream;   in    B,    forty   acres   of   ponds, 

planted  and  under  control. 
Devoted  to  land  crops,  in  A  'none, — it  is   all   too    wet    and    sour;   in    B,    all    the   made   land 

between  the  ponds. 

that  are  to  eat  it.  This  is  a  suggestion  for  the  application 
of  the  principles  discussed  in  the  earlier  pages  of 
this  chapter.  There  is,  of  course,  nothing  original 
about  it:  it  is  what  has  made  modern  animal  hus- 
bandry possible.  It  has  not  been  applied  to  fish  cul- 
ture, however,  and  we  are  not  able  to  give  any  figures  of 
production  because  it  has  not  been  tried  out  in  a  practi- 
cal way  even  on  such  a  scale  as  is  here  shown. 

Swamp  Reservations — Now,  having  presented  apian 
for  complete  utilization  of  the  marshes,  we  hasten  to 
add  that  we  believe  it  would  be  a  great  misfortune  if 


Swamp  Reservations  409 

all  the  marshes  were  to  be  ' 'improved."  Some  of  them 
are  already  serving  their  best  use  as  refuges  and  breed- 
ing grounds  of  wild  water  fowl.  In  all  of  them  there  is 
a  whole  wonderful  fauna  and  flora  that  we  could  ill 
afford  to  lose.     That  these  would  be  lost  under  an 


Fig.  243.  Wall  painting 
from  an  ancient  Egyptian 
tomb  showing  the  plan  of  a 
house  with  a  water-garden. 
(After  Brinton). 

intensive  water  culture  is  highly  probable  (see  fig.  244), 
for  our  own  cultivated  crops  are  in  the  main  successful 
about  in  proportion  as  we  eliminate  the  wild  to  make 
room  for  them. 

Since  the  wet  land  is  almost  the  last  of  the  unoccupied 
land  remaining  near  to  the  centers  of  human  habitation. 
and  since  it  is  the  dwelling  place  of  the  largest  remnant 
of  native  wild  life,  we  should  not  be  taking  measures  ft  >r 


410 


Inland  Water  Culture 


Fig.  244.     A  pond  at  Lake  Forest,  111.,  containing  islands  covered  by  butl 

For  effects  of  grazing,  d 


making  it  over  to  cultural  uses  without  at  the  same  time 
providing  reservations  where  the  wild  species  may  be 
preserved  for  future  generations.  Each  of  these  wild 
species  is  the  end  product  of  the  evolution  of  the  ages. 
When  once  lost  it  is  gone  forever:  it  can  never  be 
restored.  We  are  not  wise  enough,  nor  far  sighted 
enough  to  know  whether  the  qualities  lost  with  it  would 
ever  be  of  use  to  our  posterity.  We  are  now  only  at 
the  beginning  of  knowledge  of  our  plant  and  animal 
resources. 

But  quite  apart  from  any  possible  economic  values 
that  these  creatures  of  the  wild  may  possess,  they  have 
other  values  for  us  that  we  should  not  ignore.     Ere 


Swamp  Reservati 


012  S 


411 


1  and  divided  by  a  pasture  fence. 
:  the  extreme  ends. 


The  left  hand  end  is  closely  pastured  * 


their  destruction  is  complete,  public  reservations 
should  be  made  to  preserve  the  best  located  of  the 
marshes  for  educational  uses.  As  we  have  need  of 
fields  and  stock-pens  because  we  must  be  fed,  so  also 
we  have  need  of  this  wild  life  because  we  must  be 
educated.  It  was  with  our  forefathers  in  their  early 
struggles  to  establish  themselves  in  the  New  World: 
it  conditioned  their  activities,  lending  them  succor  or 
making  them  trouble.  In  its  absence  it  will  be  harder 
to  comprehend  their  work.  The  youth  of  the  future 
has  a  right  to  know  what  the  native  life  of  bis  native 
land  was  like.     It  will  help  to  educate  him. 


412  Inland  Water  Culture 

Exploitation  is  reaping  where  one  has  not  sown. 
Mere  exploitation  is  but  robbing  the  earth  of  her 
treasures.  Usually  it  enriches  only  the  robber,  and  him 
but  indifferently.  Getting  something  for  nothing  usu- 
ally does  not  pay.     It  tends  to  rob  posterity. 

Exploitation  is  the  method  of  a  bygone  barbarous 
age — an  age  when  men,  emerging  from  savagery, 
acquire  dominion  over  earth's  creatures  ere  attaining 
to  a  sense  of  responsibility  for  their  welfare. 

Conservation  is  the  method  of  the  future.  It  means 
greater  dominion  and  completer  use,  but  it  also  means 
restraint  and  regard  for  the  needs  of  future  generations. 
We  are  urging  that  in  the  use  of  our  aquatic  resources, 
the  wasteful  methods  of  exploitation  be  abandoned; 
and  in  two  directions: 

i.  We  urge  that  water  areas,  adequate  to  our 
future  needs  for  study  and  experiment,  be  set  apart 
as  reservations  and  forever  kept  free  from  the  dep- 
redations of  the  exploiter,  and  of  the  engineer. 

2.  We  urge  that  in  those  areas  which  are  to  be  made 
to  contribute  to  human  sustenance,  the  wasteful, 
destructive  and  irresponsible  practices  of  the  hunter  be 
abandoned  for  the  more  fruitful  and  fore-looking 
methods  of  the  husbandman. 


BIBLIOGRAPHY 

(B)  at  end  of  a  citation  indicates  a  comprehensive  bibliography. 

Adams,  Chas.  C,  and  others.     1909.     An  ecological  survey  of  Isle  R ovale, 

Lake  Superior,     pp.  468.     Rept.  Biol.  Surv.  Mich.  (B)  " 
Adams,  Chas.  C.     1913.     Guide  to  the  studv  of  animal  ecologv.     New  York 

PP.  183.  (B) 
Aldrich,  J.  M.     1912.     The  biology  of  some  western  species  of  the  Dipterous 

genus  Ephydra.     Jour.  N.  Y.  Ent.  Soc.  2077-99.     3  pis. 
Aldrich,  J.  M.     191 3.     Collecting  notes  for  the  Great  Basin  and  adjoining 

territory.     (Dipt.)  Ent.  News.  24:214-221.     (B) 
Alexander,  C.  P.  and  Lloyd,  J.  T.     1914.     The  biology  of  the  N.  A.  craneflies 

(Tipulidae,  Diptera)  I.  The  genus  Eriocera  Macquart.  Pomona  Jour,  of 

Entomology  and  Zoology.     6:12-34.     3  pis. 
Alexander,  C.  P.     1914.     Biology  of  N.  A.  Craneflies.     (Tipulidae,  Diptera). 

II.  Liogma  nodicornis  Osten  Sacken.     Ibid.  6:105-118. 

1915.     III.  The  genus  Ula  Haliday.     Ibid.  7:1-8. 

1915.     IV.  The  tribe  Hexatomini.     76^.7:142-158. 
Allen,  A.  A.     19 14.     The  red- winged  blackbird:  a  study  in  the  ecology  of  a 

cat-tail  marsh.     Proc.  Linnaean  Soc.     New  York.     43-128.     22  pis.  (B) 
^Allen,  T.  F.     1888-94.     The  Characeae  of  America.     New  York. 
Allen,  R.  W.     1914.     The  food  and  feeding  habits  of  freshwater  mussels. 

Biological  Bull.  27:127-144.     2  pis. 
Andrews,  E.  A.     1904.     Breeding  habits  of  crayfish.     Amer.  Nat.  38:165- 

206. 
Baker,  F.  C.     1898-1902.     The  mollusca  of  the  Chicago  Area.     Bull.  Ill, 

Chicago  Acad.  Sci.     In  two  parts. 
Baker,  F.  C.     1910.     The  ecology  of  Skokie  Marsh  with  particular  reference  to 

mollusca.     Bull.  111.  State  Lab.  Nat.  Hist.,  8:441-497. 
Betten,    C.     1902.     The    larva    of    the    caddis-fly,    Molanna  cinerea  Hagen. 

Jour.  N.  Y.  Entom.  Soe.  10:147-154. 
'Birge,  E.  A.     1895-6.     Plankton  studies  on  Lake  Mendota.     Trans.  Wise. 

Acad.  Sci.     10:421-484:  5  pis.,  and  11:274-448.     2j  pis. 
Birge  and  Juday.     1909.     A  summer  resting  stage  in  the  development  of 

Cyclops  bicuspidatus.     Trans.  Wise.  Acad.  Sci.  16:1-9. 
Birge  and  Juday.     1911-1914.     The  inland  lakes  of  Wisconsin. 

191 1.     The  dissolved  gases  of  the  water  and  their  biological  significance. 

Wise.  Geol.  and  Nat.  Hist.  Survey,  Bull.  22. 

1914.     Hydrography  and  Morphometry.     Ibid.  Bull.  27. 
Braugr,  A.     1909.     Die   Siisswasserfauna   Deutschlands.     19   vols.     By   $2 

authors. 
Calvert,  P.  P.     1893.     Catalogue  of  the  Odonata  (dragonflies)  of  the  vicinity 

of  Philadelphia.     Trans.  Am.  Ent.  Soc.  20:152-272.     2  pis. 
Carpenter,  W.  B.     1891.     The  microscope  and  its  revelations.     7th  edition. 

pp.  1099.     Phila. 
Coker,  R.  E.     1914.     Water-power  development  in  relation  to  fishes  and 

mussels  of  the  Mississippi.     U.  S.  Bureau  Fish.  Document  Xo.  805.     W- 

28.     pis.  6. 
.Coker,  R.  E.     1915.     Water  conservation,  fisheries  and  food  supply.      Popu- 
lar Sci.  Monthly  36:90-99. 

413 


414  Bibliography 


- — Collins,  F.  S.     1909.     The  green  algae  of  Xorth  America.     Tuft's  College 

Studies,  Vol.  II,  No.  3.     (Sci.  Series). 
Comstock,  A.  B.     1911.     Handbook  of  natue-study.     Ithaca,     pp.938. 
Comstock,  J.  H.  and  Mrs.  A.  B.     1907.     A  manual  for  the  study  of  insects. 

7th  edition,     pp.  701.     Ithaca. 
Conn  and  Washburn.     1908.     The  algae  of  the  fresh  waters  of  Connecticut. 

.  Geol.  and  Nat.  His.  Survey;  Bull.  Xo.  10.     pp.  78.     pis.  44. 
Conn,  H.  W.     1905.     The  protozoa  of  the  fresh  waters  of  Connecticut.     Conn. 

Geol.  and  Nat.  His.  Survey;   Bull.  Xo.  12.     pp.  69.     pis.  34. 
Coulter,  Barnes  and  Cowles.     191 1.     Textbook  of  Botany.     New  York,   -\ 

vols. 
Cowles,  H.  C.     1901.     The  plant  societies  of  Chicago  and  vicinity.     Bull.  II. 

Geog.  Soc.  Chicago.     Also  Bot.  Gaz.  31:73-108,  145-182. 
Dachnowski,  A.     1912.     Peat  deposits  of  Ohio.     Bull.  Geol.  Surv.  Ohio.  (4) 

vol.  16. 
x  Darwin,   C.     1859.     The  origin   of  species  by  means  of  natural  selection. 

London. 
Darwin,  C.     1875.     Insectivorous  plants.     London. 
Dodd,  G.  S.     191 5.     A  key  to  the  Entromostraca  of  Colorado.     Univ.  of 

Colorado  Bull.  15:  265-298. 
-  Dudley,  W.  R.     1886.     The  Cayuga  flora.     Bull.  Cornell  Univ.  Vol.  II,  pt.  1. 
Dyche,  L.  L.     1910-1914.     Ponds,  pond  fish,  and  pond  fish  culture.     State 

I  )ept.  Fish  and  Game.     Kansas.     Part  I  on  ponds,  1910.     Part  II  on  pond 

fish,  191 1.     Part  III  on  pond  fish  culture,  1914. 
Ehrenberg,  C.  G.     1838.     Die  Infusionstierchen  als  vollkommene  Organismen. 

Leipzig. 
Embody,  G.  C.     1912.     A  preliminary  study  of  the  distribution,  food  and 

reproductive  capacity  of  some  fresh-waer  Amphipods.     Internat.  Revue 

der  gesamten  Hydrobiologie  und  Hydrographie.     Biol.  Suppl.,  Ill  Serie. 
Embody,  G.  C.     19 14.     Crustacea.     A  key  to  the  common  genera  occurring  in 

fresh  waters  of  the  Eastern  United  States.     Ithaca. 
Embody,  G.  C.     1915.     The  farm  fishpond.     Cornell  reading  courses  4:  313- 

352.     pis.  4. 
Engler  and  Prantl.     1 890-191 1.     Die  Naturlichen  Pflanzen  Familien. 
Eyferth,  B.  von.     1909.     Einfachste  Lebensformen.     Braunschweig,     pp.584. 

pis.    If). 

'Forbes,  S.  A.     1887.     The  lake  as  a  Microcosm.     Bull.  Peoria  Sci.  Assoc. 

PP-  15- 
Forbes,  S.  A.     1893.     A  preliminary  report  on  the  aquatic  invertebrate  fauna 

of  the  Yellowstone  National  Park,  Wyoming,  and  the  Flathead  Region  of 

Montana.     Bull.  U.  S.  Fish  Com.,  11:207-258,  pis.  14. 
Forbes,  S.  A.     1878.     The  food  of  Illinois  fishes.     Bull.  111.  State  Lab.  Nat. 

Hist.  1:  71-89.     pis.  14. 
Forbes,  S.  A.     1914.     Fresh  water  fishes  and  their  ecology.     Urbana.     19  pp. 

10  pis. 
Forbes,  W.  T.  M.     1910.     The  aquatic  caterpillars  of  Lake  Quinsigamond. 

Psyche  17:219-227.      1  pi. 
"Forbes  and  Richardson.     191 3.     Studies  in  the  biology  of  the  upper  Illinois 

River.     Bull.  111.  State  Lab.  Nat.  Hist.  20:482-574.     pis.  20. 
Forel,    F.    A.     1 892-1 904.     Le    Leman,    monographie    limnologique.     In    3 

volumes.     Lausanne. 
France,  R.  H.     1910.     Die  Kleinwelt  des  Sussawassers.     Leipzig,     pp.  160. 

pis.  50. 


Bibliography  a  i  g 


Friih  &  Schroeter.     1904.     Die  Moore  der  Schweiz,  mit  Berucksichtigung  der 

gesammten  Moorfrage. 

Gage,  S.  H.     1893.     The  lake  and  brook  lampreys  of  New  York.     Wilder 
Quarter-Century  Book.     Ithaca. 
.^--Grout,  A.  J.     1905.     Mosses  with  a  hand  lens.     208  pp.     X.  Y. 

Haeckl,  Ernst.     1893.     Planktonic  studies.     (Trans,  by  G.  W.  Field)  R 
U.  S.  Commissioner  of  Fish  and  Fisheries  for  1889-1891,  pp.  565  641. 

Hagen,  H.  A.  1861 .  Synopsis  of  the  Neuroptera  of  North  America. '  Smith- 
sonian misc.  collections.     Washington. 

Hancock,  J.  L.  1911.  Nature  sketches  in  temperate  America,  pp.  451. 
Chicago. 

Hankinson,  T.  L.  1908.  Biological  Survey  of  Walnut  Lake.  Mich.  (Lans- 
ing) Rep.  Geol.  Surv.,  pp.  157-271. 

Harris,  J.  A.  1903.  An  ecological  catalogue  of  the  crayfishes  belonging  to  the 
genus  Cambarus.     Kansas  Univ.  Science  Bull.,  2:51-187. 

Hart,  C.  A.  1895.  On  the  entomology  of  the  Illinois  River.  Bull.  111.  State 
Lab.  Nat.  Hist.  4:140-237,  pis.  4. 

Hentschel,  E.     1909.     Das  Leben  des  Siisswassers.     Munich,     pp.  336. 

Herms,  W.  B.  1907.  An  ecological  and  experimental  study  of  the  Sarcophagi- 
das  with  relation  to  lake  beach  debris.     Jour.  Exp.  Zool.,  4:45-83. 

Herrick,  C.  L.  and  Turner,  C.  H.  1895.  Synopsis  of  the  entomostraca  of 
Minnesota.  Geol.  and  Nat.  His.  Survev,  Minn.,  Zool.  Series  II.  pp.  337. 
pis.  81. 

Holt,  W.  P.  1909.  In  "An  ecological  survev  of  Isle  Royale,"  (see  Adams, 
'09). 

Howard,  A.  D.  1914.  Experiments  in  propagation  of  fresh-water  mussels  of 
the  Quadrula  group.  U.  S.  Bureau  Fish.  Document  No.  801.  pp.  52. 
pis.  6.     (B) 

Howard,  A.  D.  191 5.  Some  exceptional  cases  of  breeding  among  the 
Unionidae.     The  Nautilus.     29:  4-1 1. 

Hudson,  G.  T.  and  Gosse,  P.  H.  1889.  The  Rotifera  or  wheel-animalcules. 
Vol.  I.  pp.  128.     15  pis.     Vol.  II.  pp.  144.     30  pis. 

Jennings,  H.  S.     1900.     The  Rotatoria  of  the  United  States.     Bull.  U.  S.  Fish 
Comm.  20:67-104. 
^-Jennings,  H.  S.     1906.     Behavior  of  the  lower  organisms.     New  York    B  . 
___ — Johannsen,  and  Lloyd,     1915.     Genera  of  plancton  organisms  of  the  Cayuga 
Lake  Basin.     Ithaca. 

Jordan  and  Evermann.     1904.     American  food  and  game  fishes.     New  York. 

Juday,  C.  1897.  The  plankton  of  Turkey  Lake.  Proc.  Ind.  Acad.  Sci.  for 
1896.     pp.  287-296.     1  map. 

Juday,  C.  1904.  Diurnal  movement  of  plankton  Crustacea.  Tr.  Wis.  Acad. 
Sci.  14:524-568. 

■ Juday,  C.     1907.     Studies  on  some  lakes  in  the  Rocky  and  Sierra  Mountains. 

Trans.  Wis.  Acad.  Sci.     15:781-794.     2  pis.  and  1  map. 

Juday,  C.     1908.     Some  aquatic  invertebrates  that  live  under  anaerobie  condi- 
tions.    Trans.  Wis.  Acad.  Sci.  vol.  XVI,  Part  I. 
*^~ Juday,  C.     1915.     Limnological  studies  of  some  lakes  in  Central  America. 
Trans.  Wise.  Acad.     Vol.  Sci.  18:  214-250. 

Kellogg,  V.  L.  The  net-winged  midges  of  N.  America.  Proc.  Calif.  Ac.  Sci. 
(3)3:187-223.     5  pis. 

Kennedy,  C.  H.  1915.  Notes  on  the  life  history  and  ecology  of  the  dragon- 
flies  (Odonata)  of  Washington  and  Oregon.  Proc.  U.  S.  Nat.  Mus.49: 
259-345- 


4i6  Bibliography 


Kent,  W.  S.     1880-1882.     A  manual  of  the  infusoria,     pp.  913:  pis.  51.  (B) 
Kerner  and  Oliver.     1902.     Natural  history    of    plants.     2  vols.  pp.    1760. 

London. 
Kofoid,  C.  A.     1903  and  1908.     The  plankton  of  the  Illinois  River.     Bull.  111. 

St.  Lab.  Nat.  His.  6:95-629.     1908,  8:1-361. 
Knauthe,  Karl.     1907.     Das  Siisswasser.     Neudamm.     pp.  663. 
Lampert,  K.     19 10.     Das   Leben  der  Binnengewasser.     Leipzig,     pp.   856. 

"Pis.  17.     2d.  edit.     (B) 
Lefevre  and  Curtis.     19 10.     Reproduction  and  parasitism  in  the  Unionidae. 

Jour.  Exp.  Zool.  9:  79-115.     pis.  5.     (B) 
Leidy,  Joseph.     1870.     Fresh-water  Rhizopods    of    North    America.     Rept. 

l\  S.  Geol.  Survey.     Vol.  XII. 
Lloyd,  J.  T.     1914.     Lepidopterous  larvae  from  swift  streams.     Jour.  X.  Y. 

Ent.  Soc.  22:145-152.     2  pis. 
Lloyd,  J.  T.     1915.     Xotes  on  Ithytrichia  confusa.     Canad.  Ent.  67:  117— 

121.      pi.    I. 

Lloyd,  J.  T.     19 1 5.     Xotcs  on  the  immature  stages  of  some  New  York  Trichop- 

tera.     Jour.  X.  Y.  Ent.  Soc.  23:  201-210.     2  pis. 
Lloyd,  J.  T.     19 1 5.     Xotes  on  Brachycentrus  nigrisoma.     Pomona  Jour.  Ent. 

and  Zool.     7:81-86,  1  pi. 
Lloyd,  J.  U.     1882.     Precipitates  in  fluid  extracts.     Proceeding  Am.  Pharma- 

ceut.  Assn.  30:  509-518.     (Also  1884  32:  410-419.) 
Lorenz,  J.  L.     1898.     Der  Hallstatter  See.  Mitt,  geogr.  Ges.  Wien.  Bd.  41. 
Leunis,  Ludwig.     1886.     Synopsis  der  Thierkunde.     pp.  1231.     Hanover. 
MacGillivray,  A.  D.     1903.     Aquatic  Chrysomelidae.     N.  Y.  State  Mus.  Bull. 

68:  288-312. 
Marsh,  CD.     1903.     The  plankton  of  Lake  Winnebago  and  Green  Lake. 

Wis.  Geol.  and  Nat.  His.  Surv.,  Bull.  No.  12,  Sc.  Ser.  3. 
Marsh,  C.  D.     1907.     A  revision  of  the  N.  A.  species  of  Diaptomus.     Trans. 

Wis.  Ac.  Sci.  15:380-516. 
Marsh,  CD.     1910.     A  revision  of  the  N.  A.  species  of  Cyclops.     Trans.  Wis. 

Ac.  Sci.     16:  1067-1134.     10  pis. 
Marsh,  M.  C     1907.     The  effects  of  some  industrial  wastes  on  fishes.     U.  S. 

Geol.  Surv.,  Water  Supply  and  Irrigation  Paper  Xo.  912.     (The  Potomac 

River  Basin),  pp.  337-48. 
Matheson,  R.     1912.     The  Haliplidae  of  North  America  north  of  Mexico. 

Jour.  X.  Y.  Ent.  Soc.  20:   157-193. 
Matheson,  R.     19 14.     Xoes  on  Hydrophilus  triangularis.     Canad.  Ent.  46: 

337-343-      1  pi. 
Meister,  Fr.     1912.     Die  Kieselalgen  der  Schweiz.     pp.254.     Pis.  48.     Bern. 
Miall,  L.  C.     1895.     The  natural  history  of  aquatic  insects,     pp.  395. 
Miall    and    Hammond.     1900.     The    Harlequin   fly    (Chironomus)    196   pp. 

Oxford. 
Moore,  Emmeline.     191 5.     The  Potamogetons  in  relation  to  pond  culture. 

Bull.  Bur.  Fisheries  33:  251-291.     17  pis.     (B). 
Moore,  J.  P.     191 2.     Classification  of  the  leeches  of  Minnesota.     Geol.  Xat. 

Hist.  Surv.  Minn.,  Zool.  Series  Xo.  5,  pp.  67-128. 
Morgan,  Anna  H.     19 13.     A  contribution  to  the  oiology  of  may-flies.     Annals 

Ent.  Soc.  Am.  6:371-413:  pis.  10.     (B). 
Nachtrieb,  H.  F.     1912.     The  leeches  of  Minnesota.     Geol.  and  Xat.  Hist. 

Survey  of  Minn.,  Zool.  Series  Xo.  V. 
Needham  and  Betten.     1901.     Aquatic  insects  in  the  Adirondacks.     Bull. 

47.      X.  Y.  State  Mus. 


Bibliography  4 1 7 


Needham  and  Hart.     1901.     The  dragonflics     (Odonata)    of   Illinoi  ,   with 

descriptions  of  the  immature  stages.     Bull.  111.  State  Lab.  Nat.  II 

1-94:  pi.  1. 
Needham   and   Williamson.     1907.     Observations   on   the  Natural  History 

of  diving  beetles.     Am.  Nat.  41 :  477-494. 
Needham,  J.  G.     1908.     Report  of  the  Entomologic  Field  Station  conducted 

at  Old  Forge,  N.  Y.,  in  the  summer  of  1905.     N.  Y.  State  Mus.  Bull.  124: 

156-248. 
-Needham,  J.  G.     1915.     General  Biology.     7th  edition,     pp.  542.     Ithaca. 
Noyes,   Alice  A.     1914.     The  biology  of  the  net-spinning  Trichopt.  • 

Cascadilla  Creek.     Annals  Ent.  Soc.  Am.     7:  251-272.     2  pis. 
Ortmann,  A.  E.     1907.     The  crawfishes  of  the  state  of  Pennsylvania.     Mem. 

Carnegie  Mus.  Pittsburgh,  2:  343-523. 
Osburn,  R.  C.     1903.     The  Adaptation  to  Aquatic  Habits  in  Mammals. 

Amer.  Nat.  37:  651-665. 
Parson,  H.  deB.     1888.     The  displacement  and  the  area  curves  of  fish.    Trans. 

Amer.  Soc.  Mech.  Engineers.     9:  679-695. 
Paulmier,  F.  C.     1905.     Higher  Crustacea  of  New  York  City.     N.  Y.  State 

Mus.  Bull.  91.     pp.  78. 
Pearse,  A.  S.     1910.     The  crawfishes  of  Michigan.     Mich.  State  Biol.  Surv.  1 : 

9-22. 
-Piatt,  Emilie  L.     191 6.     The  population  of  the  "blanket-algae"  of  fresh  water 

pools.     Am.  Nat.  49:  752-762. 
Reamur,  M.  de.     1734-1742.     Memoires  pour  servir  a  l'histoirc  dcs  u 

7  vols.     Paris.  . 

Reed   and   Wright.     1909.     The   Vertebrates   of  the   Cayuga   Lake    Basin. 

Proc.  Am.  Philos.  Soc.  48:  37°~459-  ..    ,, 

Reese,  A.  M.     1915.     The  alligator  and  its  allies,     pp.  341.   pis.  28.    \.  \  . 

and  London.  ' 

Richardson,   H.     1905.     A  monograph  of  the   Isopods  of   North   America. 

Bull.  54.     U.  S.  Nat.  Mus.     pp.  727-  .  e  T    ,      OA     „  . 

Reighard,   J.     1894.     A  biological   Examination  of  Lake  St.   Clair.     Bull. 

Mich.  Fish  Comm.,  No.  4.     60  pp.     2  pis.  and  1  map. 
Reighard,   J.     1910.     Methods   of  studying  the  habits  of  fishes     with   an 

account  of  the  breeding  habits  of  the  horned  dace.     Bull.  Bur.  I-  ish.     2  - : 

1112-1136. 
Riley  and  Johannsen.     191 5.     Handbook  of  medical  entomology,     pp.  34s. 

Ithaca.     (B)  «  t 

Rosel  von  Rosenhof,  August  Johann.     1 846-1 861.     Insecten    Belustigung. 

4  vols. 
-  Russel,  I.  C.     1895.     Lakes  of  North  America,     pp.125:     pis.  23.    B 
^Russel,  I.   C.      1898.     Rivers  of  North  America,     pp.  327.     pis.  1 7.      Ne* 
York. 
Sars,G.O.     1890-1911.     An  account  of  the  Crustacea  of  Norway,     pp.  17">. 

pis.  770.     Bergen  Mus. 
Schonfeldt,    H.    von.     1906.     Diatomaceae    Germania.     Leipzig,     pp.    203. 

Scott,ViU,  1911.     The  fauna  of  a  solution  pond,     [ndiana  Univ.  Si 

Scourfield,  D.  J.     1896.     Entomostraca  and  the  surface  film  of  water.     Jour. 

Linn.  Soc.  Zool.     25:1-9.     pis.  2. 
Scourfield,  D.  G.     1900.     Notes  on  Scapholeberis imucronatus ;and  the  si 

~        film  of  water.     Jour.  Queckett  Micr.  Club.     (2)7:  3©9  3". 


41 8  Bibliography 


Sellards,  E.  H.     1914.     Some  Florida  lakes  and  lake  basins.     6th  annual  Rept. 

Fla.  State  Geol.  Survey,     pp.  1 15-160. 

Shantz,  H.  L.     1907.     A  biological  study  of  the  lakes  of  the  Pike's    Peak 

Region.     Trans.  Amer.  Micr.  Soc.     pp.  75-98.      pis.  2. 
Sharp,   David.     1 880-1 882.     Aquatic  carnivorous   coleoptera   or  Dytiscidae. 
Trans.  Royal  Soc.  Sci.     Dublin.     Vol.  II.     Series  II. 
—  Sherff,  E.  E.  "  1912.     The  vegetation  of  Skokie  Marsh.     Bot.  Gaz.,  54:  415- 

435- 
Shelford,  V.  E.     19 13.     Animal  communities  in  Temperate  America.     Chi- 
cago,    pp.  362. 
Smith,  J.  B.     1904.     Mosquitoes  and  their  habits,  life  history,  etc.     Rep.  X.J. 

Exp.  Sta. 
Smith,  Lucy.     191 3.     The  biology  of  Perla  immarginata.     Ann.  Ent.  Soc. 

Amer.  6:  203-211.     1  pi. 
Snow,  Julia  W.'    1902.     The  Plankton  algae  of  Lake  Erie.     Bull.  U.  S.  Fish. 

Comm.     22:  371. 
Steuex,  A.     1910.     Planktonkunde.     pp.  723.     Leipzig. 
Stokes,  A.  C.     1888.     A  preliminary  contribution  toward  a  history  of  the 

fresh-water  Infusoria  of  the  United  States.     Jour.  Trenton.     Nat.  His. 

Soc.     Vol.  I.     No.  3. 
— Slakes,  A.  Q.     1896.     Aquatic  microscopy  for  beginners,     pp.326.     3d  edit. 

Trenton. 
Strodtman,     1898.     Ueber  die  vermeintliche  Schadlichkeit  der  wasserbliithe 

Forschungsber.     Biol.  Sta.  Plon.     6:  206-212. 
Surber,   T.     1912.     Identification   of  the   glochidia   of  freshwater  mussels. 

U.  S.  Bureau  Fish.  Document  No.  771.     pp.  10.     3  pis.     Also  1915  Docu- 
ment No.  813.     pp.  9.     1  pi. 
Swammerdam,  Johannes.     1685.     Historia  insectorum  generalis.     pp.  212. 

pis.  13. 
Tilden,  Josephine.     19 10.     Minnesota  algae.     Report  of  Minn.  Surv.  Bot. 

Series  VIII.     Vol.  I.     pp.  328.     pis.  20. 
- — Transeau,  E.  N.     1906.     The  bogs  and  bog  flora  of  the  Huron  River  Valley. 

Bot.  Gaz.,  40:  351-428. 
Transeau,  E.  N.     1908.     The  relation  of  plant  societies  to  evaporation.     Bot. 

Gaz.,  45:  317-31- 
Ulmer,  Georg.     191 1.     Unsere  Wasserinsekten.     pp.165.     Leipzig. 
Verworn,  Max.     1899.     General  physiology.     London.     (Tr.  by  F.  S.  Lee). 
Vertrees,  H.  H.     1914.     Pearls  and  pearling.     New  York. 
Vorhies,  C.  T.     1 909.     Studies  on  the  Trichoptera  of  Wisconsin.     Trans.  Wise. 

Acad.  Sci.     16:647-738.     10  pis. 
Walton,   L.   B.     1915.     Euglenoidina,   Ohio  State  Univ.   Bull.     Vol.   XIX. 

No.  5. 
Ward,   H.   B.     1896.     A  biological   examination   of  Lake   Michigan  in  the 

Traverse  Bay  region.     Bull.  Mich.  Fish.  Com.  Xo.  6,     pp.  100.     pis.  5. 
*f Ward    and    Whipple,     editors.     (In   press)    American    fresh-water   biology. 

Chapters  by  many  specialists.     (B) 
-f- Warming,  E.     1909.     Ecology  of  plants.    An  introduction  to  the  study  of 

plant  communities.     Oxford.     (Transl.  by  Percy  Groom). 
Weckel,   Ada  L.     1907.     The  fresh-water  Amphipoda  of   North   America. 

^ Proc.  I'.  S.  Nat.  Mus.,  32:  25-58. 

^"      Weckel,  Ada  L.     1914.     Free-swimming  fresh-water  Entomostraca  of  X;orth 

America.     Trans.  Amer.  Mic.  Soc.  33:   165-203.      (B) 
Weismann,  August.     1866.     Die   Metamorphose  der  Corethra  plumicornis. 

Zeitschrift  fur  wissensch.     Zoologie,  16:  45-127,  2  pis. 


Bibliography  419 


Wesenberg-Lund.     1910.     Grundzuge  der  Biologie  des  Susswa   serplai 

Internat.     Rev.  Hydrobiol.  und  Hydrog.  Biol.  Stippl.   I.       zu    Bd.   Ill   . 
West,  G.  S.     1904.     A  treatise  on  the  British  freshwater  algae,     pp. 

Cambridge. 
"West,  W.  and  West,  G.  S.     1904-1908.  A  monograph  of  the  Briti 

diacese.     Ray  Society  publications.     Vol.  1.     pp.224,     pis.  32.       B 

Vol.  II.     pp'  204.     pis.  64;  Vol.  III.     pp.  273;  pis.  95.       I; 
^Whipple,  George  C.      1914.     The  microscopy  of  drinking  water.      Ww 

and  London.     3d.  edition,     pp.  409,  pis.  19. 
Williamson,  E.  B.     1900.     Tbe-dragonnies  of  Indiana.     24th  Ann.  R 

Dept.  Geol.  and  Nat.  Resources  Ind.  j3p.  229-233. 
Wolcott,  R.  H.     1905.     A  review  of  the  genera  of  the  water  mites.     Trans. 

Am.  Micro.  Soc,  pp.  161-243. 
- — Wolle,  Francis.     1887.     Fresh-water  algas  of  the  Unite! ]  States.     Vol.1,     pp. 

364:  Vol.  II.     pis.  210. 
Wolle,  Francis.     1892.     Desmids  of  the  United  States,     pp.182,     pi 
>Wolle,  Francis.     1894.     Diatomacae  of  North  America,     pp.  45.     pis.  112. 
Wright,  A.  H.     1914.     North  American  Anura:  life-histories  of  the  Anura  of 

Ithaca,  N.  Y.     Carnegie  Inst.  Pub.  No.  197.     pp.  98.     pis.  2\. 
Zacharias,  O.     1891.     Die  Tiere — und  Pflanzenwelt  des  Susswassers.     Leip- 
zig- 
Zacharias,  O.     1907.     Das  Siisswasserplankton.     Leipzig. 
Zacharias,  O.     1909.     Das  plankton.     Leipzig,     pp.  213. 


Much  additional  limnological  work  has  appeared  in  the  Transactions  of  the 
American  Microscopical  Society;  Transactions  of  the  Wisconsin  Academy 
Sciences;  American    NaturaHst;  Botanical    ftazptfr,:  Bulletin    Illinois 
Laboratory  of  Natural  History;  Annales  de  Biologie  Lacustre;  annales  de 
la  Station  Limnologique  de  Besse;  Archiv.  fur  Hydrobiologie  u.  Plankton  - 
kunde,  (formerly  Forschungs-berichte  aus  der  biologischen  Station  zu  I 
Biologisches  Centralblatt ;  Nature;  Transactions  of  the  Linnasan  Soci 
London;  Zeitschrift  fur  wissenschaftliche  Zoologie,    Zoologischer    An 
Zoologisches  Jahrbucher,  and  other  current  biological  journals. 

The  seven  general  limnological  works  that  we  regard  as  most  useful 
Ward  and  Whipple,  in  press;  Brauer,   1909;  Stokes,   1896;  Whipple.    [914; 
Eyferth,  1909;  Lampert,  1910;  and  Steuer,  1910. 


Page  24 

Page  25 

Page  59 

Page  76 

Page  77 

Page  89 

Page  99 

Page  100 

Page  158 

Page  242 

Page  281 

Page  282 

Page  293 

Page  314 

Page  315 

Page  375 

Page  377 

Page  379 

Page  401 

r    r    f    r    r    f    r 


LIST  OF  INITALS   AND  TAIL-PIECES 

Primrose  Falls,  Fall  Creek,  Cornell  University  Campus. 
Coy's  Glen  near  Ithaca:  upper  falls. 
Lake  Temagami,  Ontario,  Canada. 
A  "carry"  between  lakes. 
Buttermilk  Creek  near  Ithaca. 

Pond  in  the  Montezuma  Marshes,  Central  New  York. 
Six  mile  Creek  near  Ithaca. 
A  spray  of  Buttonbush. 
Water  Shamrock  and  Water  Spider. 
Pool  at  foot  of  Primrose  Falls,  Fall  Creek. 
Maligne  Lake,  British  Columbia.     (Photo  by  J.  C.  Bradley.) 
Coy's  Glen  at  the  mouth. 
Gorge  of  Six  Mile  Creek  near  Ithaca. 
Williams  Brook,  near  the  Cornell  U.  Biol.  Field  Station. 
The  Staircase  Falls,  Coy's  Glen. 

Sunfish  swimming.     Photo  by  Dr.  R.  W.  Shufeldt.     From 
the  Nature-Study  Review. 

Duck  Creek,  near  Cincinnati,  Ohio. 

Shocked  Cat-tail  Flags  on  the  Montezuma  Marsh. 

Lowermost  fall  of  Buttermilk  Creek  near  Ithaca. 


INDEX 


PAGE 

aborigines 382 

acids,    humous 95,  96,  348 


Acilius 


333 


Acorus 157 

Acroperus  harpae 300,  301 

adaptations 260,  274,  277 

Adineta 299 

adjustment 248,  261 

adjustments,  individual 242 

"  mutual 242,  282 

adjustability  to  waves 319 


aeration 


73 


Agassiz,  Louis 19 

Agraylea 216 

agriculture 379,  402 

agricultural  crops 404 

air-breathing    231 

air-chambers 275,  277 

air-spaces 265',  271 

air-tubes 279 

albumins 48 

ajder: 158,351,352 

ale-wives 232,  373 

algae,  26,  28,  29,  45,  46,  72, 
100,  101,  102,  no,  119,  137, 
J44,  H5,  151,  169,  180,  181, 
183,  189,  217,  220,  223,  295, 
296,  301,  302,  304,  307,  311, 
322,  391,  345,  356,  362,  373, 
390,  395 

algae,  "blanket" 336,  345,  399 

blue-green 

109,  132,  297,  302,  326 
filamentous  blue-green  296,  310 

brown 135,  136 

fresh  water 101 

free-swimming 28,  339 

gelatinous   101 

green 124,  129,  299,  302 

filamentous  green 124 

plancton 50,  244,  392 

protococcoid  green 318 

lime-secreting 50 

marine  135 

of  ponds 335 

red 135,  136 

sessile 120,  126,  336 


algae,  siphon    l2l 

slime-coat    

tufted iI2i  i2< 

unicellular j  ut    ]2,, 

Allen,  Arthur  A <,^  *a2 

Alismaceae '  ',  -,". 

Alisma »*, 

alligators 

Amby stoma  tigrinum 237,   $42 

ammonia 25,  48,  49,'  140 

Amoeba icn 

amphibians.  .  .  148,  231,  236,237,  337 

Amphipoda 189,  [9 

Amphizoidae    224 

Anabaena  132,    133,   295,   296,    29*7, 
A        ,      .    305,   308,   392 

Anachans 1  =; 

Anapus 

A*ax;--. 155,34 

Junius 196 

Ancylus 182,  260,  370,  373 

Andromeda 1 ; 

angling 407 

animalcules 295 

animal  forage 

animal  husbandry 3S4,  400,  408 

animals,  hoofed .  . 312 

animals,  limpet-shaped 260 

animal  life  of  marshes 345 

animal   population 

animals,  warm-blooded 

Ankistrodesmus  falcatus    129 

setigeru^.  .  .  129,   i  ;  1 

Anodonta 1  8< 

edentula 

"  grandis 

"  imbecillus    

antennae 185,  1  89,  2  \~.  251,  312 

Anthomyid   fly 

Anthophysa 

Anthony,  Maude  H 214,  215 

Anuraea 299,  J 

Aphanizomenon 297, 

apical  buds 154, 

Appalachian  hills 

applied  science 21 

Apsilus    


421 


422 


Index 


PAGE 

Apus 184,263,318 

aquaria 165,    [70 

aquatic  animals 180 

"      bryophytes 148 

'       carnivores 327 

caterpillars.  .  .  .219,  220,  398 

collecting    19 

Diptcra 346 

"       environment 25 

"       fernworts    149 

herbivores 190,  396 

insects 158,  195,  276 

larvae   236 

"       locomotion 273 

"       mammals.  .158,241,270,  273 

microscopy 19 

organisms 99,  389 

"       resources  . 412 

"       rodents 153 

11       seed-plants 151,  307 

"       societies 282,  293 

aquatics,  broad-leaved 154 

emergent  1 5 1 ,  32 1 ,  334,  339, 

341 

floating 334,  339 

rooted 334 

submerged  94,  1 1 5,  32 1 ,  339 

345 

surface 321,334 

Arcella 159,  160,  299 

armor    246 

armor,  chitinous 183,  251 

aroids    157 

arrow-heads  .  .272,  334,  345,  380,  405 

Arthropods 183 

arum,  arrow.  .  .  157,321,  334,  380,405 

Asclepias  incarnata 345 

Asellus 190,  191,  192,  253,  340 

aspens 378 

Asplanchna 248,  299 

Asterionella  in,  114,  245,  297,  303, 
305,  308 

Atax  crassipes 301 

Azolla 150,  151,  153,282,334 

Bacillus 140 

bacillus,  typhoid 141 

back-swimmers 211,  276 

bacteria  20,  48,   100,   139,   141,  296, 
390 

chromogenic 140 

"         iron  142 


PAGE 

bacteria  nitrifying 140 

"        sulfur 143 

bacterial  jelly 140 

Baetis   360 

balancers 370 

Baltic    18 

barometric  pressure 73 

barrier  reefs 73 

bars,  building  of 85 

basins 59,65,67,71,356 

bass 233,291,399 

Batrachospermum 136 

bayous 169,  334 

bays 307 

beach 73,  81 

beaver 241,  274,  377,  378 

beetles  195,  220,  275,  276,  277,  281, 
318,  346 

beetles,  adult  338 

"       diving.  .  .  .221,  222,  275,  276 

gyrating   407 

Parnid 260,  359,  367 

"       riffle 224,  259 

whirl-i-gig 221,  338 

Beggiatoa 142,    143 

Belostoma 211 

Benacus 210,  211,  212,  276 

Betten,  Cornelius 258 

bicarbonates 51 

Bidessus   333 

Biological  Field  Stations,  Ameri- 
can  22,  23 

Biological  Field  Station,  Cornell 

University,  65,  87,  95,  266,  330, 

335,  397 
Biological  Lab.,  Fairport  23,  79,  291 

birches 378 

birds 231,239,249,390 

Birge,  E.  A.,  36,  37,  38,  43,  44,  46,  47, 
51,  53,  65,  66,  72,  263, 
304,306,310,391 

bitterling 292 

bittern 342 

bivalve 180,  185,288 

blackbird,  red- winged 342 

black-fly 227,264 

bladders 265,  284 

bladderworts,  155,  264,  271,  272,  283, 
284,285,286,319,405 

blanket-moss    120 

Blasturus 120,  345,  398 

Blepharoceridae 228 


Index 


423 


PAGE 

Blepharocera 259,  367 

bloodworms,  106,  250,  254,  279,  280, 
3io,  394,  395,  398 

blubber 273 

bog  cover 348,  349,  350,  35 1 

bog-moss.  .89,  145,  146,  147,  348,  349 

bog-pond 352 

bog-pools    129 

bogs,  53,  89,  90,  94,  95,  115,  146,  149, 
152,  155,348,351 

bogs,  climbing 94 

bogs,  peat 117 

bogs,  sphagnum 52,  64,  157 

bogs,  upland 156 

Bosmina .  .  185,  248,  249,  301 ,  328,  329 

Botryococcus 129,   299 

Botrydium 121 

bottom,  false 54 

bottom  herbage 334 

bottom-lands,  alluvial 67 

bottom,  black  muck 115 

bottommud,95, 106, 133, 154,243, 252 
bottom  ooze.  .  .48,  159,  181,  191,  235 

bottom  population 327 

bottom  slime 133 

bottom  sprawlers 254,  340 

Boyeria 360 

Brachionus 178,  179,  299 

Brachycentrus 363,  364,  366 

brambles 351 

Branchiopods.  .  .183,    184,    185,    263 

Brasenia 334 

Brinton,  D.  G 409 

bristles 246,  248 

brood-chamber 187,  267,  288 

brood-pouch 190,  191,  393 

Brook,  Lick,  Ithaca 317 

Williams,  Ithaca 358 

brooks 77,8i,  167,  170,333,356 

Bryophytes 146 

Bryozoans,  166,  169,  247,  266,  269, 
325,  332,  335,  34i 

buck-bean 345 

buds,  over-wintering 264 

buffalo  gnat 364 

bugs. 210,  277 

bullheads 345,  3§8 

bull-frogs 14,  236 

bulrush 319,  334,  343 

buoyancy,  of  organisms 243,  247 

bur-reed  156,  157,  323,  334,  343,  346 

burrowing 251,  254,  257,  314,  3  *6 

burrows 254,  255 


burs 

buttons,  pearl 

Bythotrephes 51  >i 

Caddis-flies,  195,  197,  200,  214,  218, 
2.S'S,  260,  .  341, 

345,    36<),   3'".  363,  37< 
Caddis- worms,    14,  84,  i<;;,  [9 

258,  260,  j', j,  . 

340,  341,  357, 

362,  3^3,  365.  370,  371- 

372,  373,  3   3,  398 
Caenis.  .  .205,  253,  340,  345,  388,  39s 

Calcium  salts 52 

Caledonia  shrimp 

calla [57 

Callibaetis 341,  3o<>,  397,  398 

Calyculina    341 

Cambarus  bartoni 1 1 ;  J 

Campanula  aparinoides 344 

Campus,  Cornell  University.    .  .     42 

Campylodiscus Ill,  115 

Canthocamptus [8f 

canvas-backs 240 

capillarity 97 

Carabidae 221 

carapace 184, 192,251 

carbonates _ 

carbon  consumption 44 

carbon  dioxide  43,  44,  45,  50,  51,  72, 

139 

Carices    157 

carnivores,  18,  171,209,222,  241,  282 
283,312,318,374,3  ■■,- 

carp   22>2>,  234,  235.  3^4.  3'"' 

Carteria 103,  104,  3<>»' 

Cassandra 157,  35° 

cases,  cylindric,  of  sand  34  ' 

"      limpet-shaped 

"      portable 371 

"     stone-ballasted 371 

Castalia  odorata . 

cataract IOI 

caterpillars 

catfish 232.  233,  2* 

cat-tail  flag 01,02,  156,321 

334,343.355. 

cat-tail,   narrow-leaved 

celery,  wild 

Celithemis   

cells,  aggregated ....        H 

"      association  of I ,; ! 

11      chlcrophyl-bearing  . ...  147,  349 


424 


Index 


PAGE 

cells,  cortical    138 

"      division  of ...  112,  117,  121,  122 

"      flagellate 295,   305 

"      internodal 138 

"      multinucleate 131 

"      rectangular  blocks  of 149 

"      reproductive 12 

"      reservoir 146,  147,  349 

"      sex 105,  139,  151,  250 

cellulose    139 

cell  wall 123 

Ceratium  103, 108,  248,  296,  302,  305, 

308,337 
Ceratophyllum  134,  154,  155,  321,  334 

Ceratopogon 279 

Cercaria    174 

Ceriodaphnia 267,  268,  269,  301 

Cestodes 174 

Cetacea 273 

Chaetogaster  173 

Chaetonotus 164,  165,  166 

Chaetophora.  .  126,  127,  182,  336,  338 
chamber,  respiratory.  .  .250,  252,  253 

Chamot.E.M * 79 

Channels 59,  77,  89 

Chantransia 81,    136 

Chara  52, 137, 138, 139,  319,  322,  334, 
352 

Characeae 101,  137 

Chauliodes 213 

chemical  analysis 48 

Chirocephalus 184,  263,  318 

Chironomidae    225 

Chironomous  228,  257,  280,  329,  330, 

332,336,340,341,393, 

394,  395,  396 

Chirotenetes 259,  364,  366 

Chlamydomonas 104 

Chlamydothrix 141,  142 

Chloroperla 203,  278 

chlorophyl   no,  119,   125,   139,  265, 
271,  296 

Cholera  spirillum 141 

Chrosomus  erythrogaster 394 

Chrysops 230 

Chydorus  185,   300,   301,    303,    305, 
310,326 

Cicuta  bulbifera 345 

cilia 160,  170,  246,  250 

ciliates   246,  282,  327 

circulation  periods 35,  37,  46 

Cladocera   185 

Cladocerans  185,  300,  301,  303,  304, 
312 


PAGE 

Cladophora  8i,    112,    125,    126,    136, 
322,  336,  362 

Cladothrix    142 

clams 180 

Clathrocystis .  .  .  .297,  304,  305,  308 

Climacia 214 

climate    294 

Closterium 1 17, 119 

Clupea  pseudoharengus 232 

coastal  plain 93 

coats,  chitinous 266 

Cocconeis 115 

Cocconema   1 1 1 ,  115 

Coccus 140 

cocoon 213 

Coelambus 333 

Coelastrum 129,  130 

Coelenterates 163 

Coelospha erium 132,  133,  297 

Coleochaete 128 

Coleoptera 195,  220,  279 

colonies  dendritic    246 

"        discoid    245 

11        expanded 245 

"       radiate 245 

"        spherical 104,  107,  245 

Colurus 299 

conjugation    121 

Conjugates,  filamentous.  ...  119,  126 

conjugates 263,  299 

Conferva 124,  126,  299,  336 

Conochilus 177, 249 

conservation 21,  412 

control,  methods  of 399 

coots   342 

Copepods  183,    188,    189,   200,   246, 
263,   301,   303,   325,   328 

Coptotomus 214,   335 

Cordulegaster 360 

Corethra 108,  301,  310,  329 

Corixa 201,  276 

Corydalis 213,214 

Cosmarium 119 

Cothurnia 161,  162,  332 

crabs 183,    192 

crabs,  horse-shoe 184 

cranberry 348,  349,  350 

craneflies.229,  277,  339,  346,  358,  360 
crawfishes  175,   191,    192,   252,   340, 
342,   390 

creeks    77 

Creek,  Fall,  Ithaca 330 

Crenothrix   142 

Cristatella 169 


Index 


425 


PAGE 

crops,  diversifying  of 403 

crowfoots 156,  271 

Crucigenia 129,  130 

Crustacea  183,  189,  192,  193,  301.  302 

Crustaceans  20,     45,     52,   161,   183, 

187,  251,  253,  285,   299, 

304,  318,  340,  345,   382, 

383,  399 

Culex 280,  329 

Culicidae 227 

current 83,  85,  356 

current  meter 86,  319 

currents,  conduction 31 

convection 31,  38,  292 

descending 36 

Curtis,  W.  T 290 

cuticle 271 

Cyanophyceae 132 

Cybister   275 

Cyclops  188,  189,  244,  263,  301,  303, 
305,310,311,312 

Cyclotella 112,  114,  299 

Cylindrocystis 116,    119 

Cyperus  diandrus 207 

Cypripedium    351 

Cypris     188 

cyst 289,  290,  291,  292 

Dace 374 

Dachnowski's  diagram 352 

damselflies  195,  207,  279,   280,   281, 

332,  341,  346 
Daphne  185,  186,  248,  301,  306,  309, 
312,  391 

Daphnia 285,  292,  303,  304,  306 

darters,  least 231,  233 

darters 250,  259,  362,  374 

Darwin,  Charles 17,  18,  283,  285 

Decapoda 191 

Decodon  354 

decomposition    48 

defense    251 

deltas 60, 65 

Delta  of  Mississippi 67 

Dero 173,  174,257 

desiccation 316,318 

Desmidium 117 

^desmidssi       52,     53,  116,  117,  119, 

121,    I44,   263 

Diaphanosoma 301,  304 

Diaptomus  101,   188,   189,  301,  303, 

305,  3ii 
Diatoma 115,  245,  297 


PAGE 

diatomaceous  earths 1 10 

diatomaceous  ooze 

diatoms  29,  53,  81,  84,  101,  109,  no 
115,  144,  183,  189,  20O,  j  1 7, 
248,  297,  302,  303,  305,  311, 
362,  387,  394,  395,  399 

diatoms,  colonial 391 

"         epiphytic    \\- 

"         needle 1 1 2 

"         sessile    

"         slime-coat 322, 

"         "white-cross" 1 1 1 

diatom  rakes 373 

Dictyosphaerium [29 

Dicranomyia    359 

Didymops 340 

Difflugia 159,  257,  299,  303 

Diglena 299 

Dinobryan  101,   106,   107,  24<.. 
303,   308,   310,    337 

Dinocharis    299 

Diptera 195,  224,  337 

Diptera,  aquatic    225 

"         blood-sucking 227 

discs,  attachment    171 

"     respiratory 230 

' '      sucking 228 

dissolved  colloids 54 

distribution 266,  322,  33 

distribution,  vertical 310,  324 

ditches 133,  152,  [I 

ditch-grass    71 

Diurella 

divers 239,  241 

divers,  pearl 3° 

Dixa    329 

dobsons 213 

Docidium 1 19 

dogwood  

Dolomedcs 

Donacia 33; 

Dorosoma 

dragonilies  195,    [97, 

332,   340,   34i.   356,    389 

drainage    4n- 

Draparnaldia 124,    128 

Droseraceae 

Drosera 

drouth 97 

Dryops   

duckmeat I49i  '' 

ducks 

duckweeds.  ..  15c   153,  272.  321,  334 


426 


Index 


PAGE 

Dudley's  Cayuga  Flora 151 

dwelling-tubes  of   midge  larvae 

335,  336,  365 

Dytiscidae 222,  346 

Dytiscus 221,  222,  276,  280,  333 

Ears,  external 274 

earthworms    3IG 

lie  progress 399 

eel-grass 90.  *53,  3*9.  334 

egg-parasites    195 

eggs,  of  amphibians 237 

"    of  Benacus 211 

"    of  crawfishes 192 

"     drouth-resisting 318 

"    of   fishes 233 

"    of  leeches 176 

11     of  pike 400 

"     of  salamander 342 

"     of  snails 335 

14    of  Triaenodes 218 

"     summer 266,   267 

"     winter 2G6,  267,  268,  269 

Ehrenberg no 

Eleocharis 334 

Elmis 359,  370 

Elodea 155 

Elophila 220,  260,  272 

Embody,  George  C 191,388 

Enallagma    337 

Engler 143 

encasement 263 

Encyonema Ill,  112 

encystment  263,  289,  290,  304,  310, 

316,  361 
Entomostraca  85,  114,  183,  184,  188, 
193,  302,  304,  309,  310, 
312,  388,  390,  398 
Entomostracans   ...  .20,  52,  217,  341 

Epeorus 370 

Ephemera 255 

Ephemerella 340,  370 

Ephemerida 195,  205 

ephippium 268,  269 

epidermis 271 

epilimnion 37 

epiphytes    139 

Epischura 301 

Epistylis 161 

Epithemia 115 

Eriocera    256 

Eriophorum 351 

erosion 57,  60,  68 


PAGE 

Estheria    184, 263 

Esox   lucius 400 

Euastrum 119 

Euchlanis 299 

Eucrangonyx 191 

Eudorina 104 

Euglena.  .15,  102,  103,  104,  106,  296 

Euparhyphus 359 

Eupomotis   388 

Eurycerus 187 

evaporation  40,  55,  56,  76,  99,   100, 
247 

evolution 17,  410 

Experiment     Stations     for     fish 

culture 400 

exploitation 21,412 

Fall  Creek,  Ithaca.  .  .  .42,  79,  87,  115 

Falls,  Triphammer,  Ithaca 81 

fats 244,  273 

fauna 18,  53 

fecundity  of  fishes 235 

Felt,  E.  P 165 

females,  parthenogenetic .  .    .266,  268 

Ferguson,  W.  K 394 

ferments 1 39 

ferns    351 

fernworts 145,  153 

Fiber  zibethicus 241 

field  stations 20 

filaments,  algal 102 

filaments,  spore-bearing 319 

filter 20 

filtering 1 13 

fingerlings 384,  385 

fins    250 

"  pectoral 234 

fish's  bill  of  fare 398 

Fish  Commission,  United  States    79 
Fish    and    Game    Commission, 

New  York  State 344 

fish  culture  21,   384,   385,   387,   389, 
390,   399,  400,   408 

fish 290,  379,  383,  403 

fish  eggs 384 

fisher 241,   274 

fishes  282,  362,  386,   387,  389,  390, 

399,  404 

fish-flies 213 

fish  food  183,  189,  190,  235,  294,  390, 
391,  392,  393,  396,  397 

fish  forage 384,  386,  393,  403,  408 

fish  fry    384 


Index 


427 


PAGE 

fish  fry,  planting  of 384,  385,  386 

"        raising    385 

fish,  fresh  for  the  table 407 

fishponds 387,  396,  404 

fish  population 398 

fish  raising 404,  408 

Fissidens  julianum 148 

flagella  102,  103,  104,  105,  106,  108, 

246,  250,  310 

flagellates  102,    103,    106,    107,    246, 

248,    296,    302,    303,    305, 

306,    309,    311,    316,    356 

flagellates,  chlorophyl-bearing .  .    299 

green    104 

shell-bearing 108 

spherical    108 

winter    107 

flatworms  170,    171,    172,    173,    250, 
260,    263,    340,    370 

floats 247,  266,  284 

flocculence    295 

flood 57,  67,  75,  87 

flood   conditions 88 

flood-decline 88 

flood  plain 64,  77,  87,  356 

flood  plain  of  rivers 67 

flood  rise 88 

flora 18,  53 

Florida    59 

Floscularia 178,    299 

flotation  243,  245,  246,  247,  251,  272, 
297 

flotsam    153 

foliage 405 

food,  abundance  of 306 

"    available 304 

"     dependencies    389 

"    dissolved 26 

"     examinations    398 

food-fishes 387,  390 

food  preferences 305,  391 

11   relations 389 

foodstuffs 395,  402 

food  supply 21,  25 

Fontinalis 148 

forage  fishes 398,  399 

foragers 367 

foragers,  shelter-building 370 

foraging  grounds 57 

foraging  habits 373 

forage  organisms 396,  398 

Forbes,  Stephen  A.  70,  80,  389,  390, 
394 


^  pAGB 

ForeLF.A Mf  ?6 

forget-me-not iqc 

Fragillaria 115,  245,  297,  305,  308 

Fredericella    [66 

freezing  point 244 

frog,  bull 237 

"  green  237 

"  leopard 236,  237 

"  pickerel 237 

"  tree    237 

"  wood 237 

frogs  175,  236,  237,  343, 383, 38; 
frost-line 83 

Jun£i    ;•. 139 

fungi,  parasitic 296 

fungus 282,  400 

fur-bearers    241 

furs    379 

Galingale,  low 207 

Galium  palustre 344 

Gammarus 190,  191, 360,  392 

gas,  marsh 96 

gases  25,  40,  41,  43,  44,  45,  46,  54,  55, 
56,  244,  252,  265,  279,  309 

gases,  noxious 96 

Gastropus 299 

gars 291,333 

geese 239,  240,  242 

gelatin 127,  161.  [69 

gemmules 164,  247 

gill  arches 313 

"  cavity 292 

"  chambers 209,  2^2 

"  covers 253,   .;<  6 

gill-plates 208,  251 

gill-rakers 235,    31  j 

gill-strainers 392 

gills  182,  217,  233,  235,  236.  252,  273, 
275,  279,  280,  288,  369,  370,  397 

gills,  anal    

"     blood    279 

"     filamentous 204,  22 :. 

"     mussel    Is! 

"     tracheal 278,  27'-. 

"     tube 280, 

glacial  period 

glaciation    

glands   

Glenodinium 103, 

glochidia  181,  287,  288,  289,  290,  291 

Gloiotrichia 297, 

Glyceria    334 


428 


Index 


PAGE 

Goera    37* 

goldfish 384,   399 

golden  shiner 235,  387,  399 

goldthread    351 

Gomphines 209,  254,  357 

Gonatozygon 117,  119 

Goniobasis    37° 

gonidia    I41 

Gonium 104 

Gordius 174 

gorges,  post-glacial 64 

gradient  of  channel 85 

gravel,  deposits  of 42 

gravity,  specific 243,  244,  246 

grebes    342 

grouping  by  levels 326 

Grout,  A.  J 148 

gulls 239 

Gyrinidae 221 

Gyrinus 337 

Gyrosigma   112 

1 

Habenaria 35 

habitat    294 

Haeckel,  E 392 

haemoglobin 253 

Haemopsis   175,  176 

hairs 248,  274 

hairs,  glandular 283,  285 

Halesus  guttifer 198,  361 

Haliplidae 223,  275,  346 

Haliplus   277 

hand-net 20 

Hankinson,  T.  L 231,  233 

Harper,   Francis 93 

hatcheries 384,  385,  400 

Hawkins,  L.  S 321 

Headlee, T.J 324 

heaths 157,  35i,  355,  357 

Helicopsyche 370,  372,  373 

hellgrammite 214,  313 

Hellriegel    56 

Hemerobiidae 212,  214 

Hemilastena 291 

Hemiptera 195,  210,  274 

hemp-weed,  climbing 345 

Heptagenia 278,  368,  370 

herbivores  18, 128,  153,  180,  186,  282, 
318,373,389,390,392 

herring 291,  313 

herons 239 

Heterocope 311 

Hexagenia 115,  255,  341,  398 


PAGE 

hibernacula 264,  265,  272 

hibernating 269 

Hibiscus    145, 405 

Holopedium 52 

hooks 247,  266 

hornwort.  134,  154,  155,  271,  272,  334 

horseflies 227,  254 

horse-leeches 175,  250 

host  species 291 

Howard,  A.  D 289,  291 

huckleberries 351 

humid  regions 55,  56 

humus 57 

husbandry 385,  386,  412 

Hyalella    191 

Hydatina 299,  305 

Hydra  163,  164,  282,  325,  327,  332, 

341 

Hydrachnidae    193 

Hydrocampa 218,  257,  337 

Hydrodictyon 122,  124 

hydrogen  sulphide 47,  96 

Hydrohypnum 358 

hydromechanics 107 

Hydrophilidae 222,  276,346 

Hydrophilids 221,  222 

Hydrophilus 275 

Hydroporus   222,  333 

Hydroptilidae    216 

Hydroptila  258 

Hydropsychidae    217 

Hydropsyche.  .218, 363, 364, 365, 370 

hydroxide  of  iron 142 

Hydrurus   136 

Hymenoptera 195 

Hypericum  virginicum 344 

hypnums 148,   149 

hypolimnion 37 

Ice 35,36,  80,  81,  120 

ice,  anchor 82,  83 

ice,  floes 61 

ice  in  streams 81 

ice  rubble 81,  82 

Ignis  fatuus 96 

Illinois  State  Laboratory  of  Na- 
tural History 50,  79 

infusoria 171,179 

inclusions   244 

increase,  rapidity  of 306 

incrustations  of  lime 251 

Indianapolis  News 384 

Indians 13 


Index 


429 


PAGE 

insects  183,  251,  274,  357,  358,  367, 
390,  399 

insects,  aquatic   338 

gall 291 

"        herbivorous 398 

net-winged 195,  212 

"        plancton-gathering   ....   364 

internodes 138 

inundation   88 

iris 404 

iron   53 

iron  sulphate 95 

Isoetes 151 

Isopoda 190 

Ischnura  verticalis 207,  208 

Ithytrichia 260,  262,  372 

Jack-o-lantern 96 

Jagerskiold 172 

Johannsen,  O.  A 299 

jointweed    345 

Jo-pye-weed 323 

Juday,  C.  36,  37,  38,  43,  44,  46,  47, 

51,53,  72,263,308,312 
Juncaceae 157 

Kent    309 

Kirchnerella 129,    131 

Knight,  H.  H 75,  196,  350 

Kofoid  C.  A.  22,  48,  83,  85,  88,  103, 

107,  113,  130,  131,  164, 

171,312,  356 

Laccophilus    , 333 

lace-wings 214 

lagoons   334 

Lake  Alachua 69 

"     Canandaigua    65 

11  Cayuga  28,  32,  36,  42,  60,  64, 
65,  73,  114,  123,  151, 
218,  232,240,  295,  296, 
300,  308,309 

Lake  Coeur  d'Alene,  Idaho 60 

Devil's,  Wisconsin 51,  71 

Erie  63 

Evans'   Michigan 62 

Flag 312 

Flathead 71 

Fure,  Denmark 28 

Geneva 28,  76 

Great  Salt 71 

Green 63 

Hallstatter,  Austria 33 


PAGE 

Lake  Huron  63 

"     Kegonsa   66 

"     Keuka 64,  65 

"     Knight's 44 

"     Louise,  B.  C 60 

"     Mendota  37,  38,  46,  47,  66,  304, 
306,310 

Miccosukee 69 

1     Michigan  .  .28,  61,  63,  114,  312 

"     Monona    66 

"     Okoboji 71 

"     Ontario 63 

11     Otisco 65,  72 

"     Owasco 65 

"     Pepin 67 

"     Phelps 57 

"     Pontchartrain    67 

11    Quiver 49,  164 

"     Seneca 65 

"     Silver 71 

"     Skaneateles 6s,  7- 

"     St.  Clair    28 

"     Sumner,  Isle  Royal 54 

"     Superior 63,  73 

11     Tahoe 28,60 

"     Thompson's 49 

"     Turkey    312 

"     Wabesa 66 

"     Walnut 161,233,239 

"     Winona 71,   324 

"     Yellowstone 70 

lakes  .59,  60,  231,  232,  299,  307,  316, 
333,  356,  406 

"     alkaline  or  salt 74 

"     crater 60 

' '     currents  in 7  \ 

"     depth  of 7  I 

Lakes,  Finder 64,  65 

lakes,  floodplain 67 

"     of  Florida 69 

"     Fulton  Chain  of 165 

Lakes,  The  Great 61,  63,91.  3<>1 

lakes,  playa    75 

"      polar 

"      solution ' 

"      strand 75 

"      Swiss    7° 

"      of  Wisconsin 66 

"      of  Yahara  Valley 

"      stagnation  periods  of .  .  .    34.  4" 

Lakeside  Biological  Laba 

7*'.  71 

Lampsilis 290,  291,  324.  3*5 


430 


Index 


l'AGE 

larvae,  of  black  flies 227,  364 

of  beetles 120,250,368 

"        of  caddis-flies 215 

"        of  craneflies 256 

dipterous 224,  227,  288 

of  fish-flies 213 

of  horseflies.  .  .  .227,  230,  340 

of  mayflies 120,  332 

of  midges  226,  227,  250,  258, 
325,  338,  341,  356, 
373,  387,  388,  389, 
390,  393,  394,  397 

11       of  mosquitoes 227,  250 

of  orl  flies 213 

"       of  punkies 120 

"       of  spongilla  flies 215 

leaf-beetle 34° 

leaf-drift 360 

leech,  clepsine 17° 

leeches,  171,  175    176,  257,  325,  341, 

364 

Leersia    344 

Leeuwenhoek 16 

Lefevre,  G 290 

Leidy,  Joseph 19 

Lemanea 135,  J36 

Lemnaceae 135 

Lemna 150,  173,  240,  321,  334 

Lepidoptera I95,2i8 

Leptidae,  aquatic 229 

Leptoceridae    216 

Leptocerus 216,260,372 

Leptodora 301,  311,  312 

Leptophlebia   36° 

Leptothrix 141  -  142 

Lestcs 341,345,346 

Leunis 173 

Libcllula 34° 

lichens 132,  282 

life  cycle 260,261,274,316,397 

life,  on  the  bottom 326 

"    at  the  surface 327 

"    in  open  water 243 

light 306,  307,  308 

light  relations 29 

Liljeborg 18 

Lime   50 

limestone 5° 

Limnaea 182 

Limnacea   34^ 

Limnephilus 197,  198,  199,  200 

Limnobates    346 

Limnocalanus 301,  311 


PAGE 

Limnochares 194 

limnological  phenomena 14 

Limnophilus 345 

Limnophora  359 

limpet 260 

Lintner,  A.  J 214 

liverworts 146,  153,  334 

lobsters 192 

locomotion 273,  281 

locomotion,  rolling 104,  107 

locn    239 

Lorenz 33 

lorica 106,  161,  178 

loricate  forms 299 

lotus 380,  404 

Lloyd,  J.  U 54 

lubrication    _ 272 

Ludvigia   palustris 156 

lungs 275,276 

Lyman,  Helen  Williamson 214 

Lyngbya 297,   305 

Mackerel 250 

Macrobiotus 164,  166 

Magazine,  Farmers' 384 

maggot,  rat-tailed 229,  277,  339 

magnesia 50 

Malacostraca 183,  189,  301 

Mallomonas 299,  308,  309 

Malpighi 16 

mammals 231,  273,  274 

Mammoth  Cave,  Kentucky.  ..  .51,84 

manna  grass 334,  343 

mantle 252 

marl 5°,  75-  352 

marsh  bedstraw 344 

"       bellwoxt 344 

"       fern 145,344 

"       five-finger   344 

gas 48 

horsetails    151 

"       mallow    145 

Montezuma 65,87,91,92 

"       ponds 95 

Renwick,  Ithaca 347 

skull-cap 344 

"       St.  John's  wort 344 

marsh-treadcr    346 

marsh-wren    342 

marshes  14,     48,     59,     64,     65,     66, 
73,     <s9,     90,     95,     97,  263, 
307,  3i6,  333,  345,  346,  402, 
411 


Index 


43 1 


PAGE 

marshes,  Canoga 318 

cat-tail 91,  240,  241 

fresh- water 90 

utilization  of 408 

Marsilea  134,  149,  321,  323,  334,  407 

marten    241 

Mastigophora 102 

Matheson,  Robert. 222,  223,  277,  317 

mating  nights 206 

matter,   dissolved 26 

matter,  suspended 26,  42 

mayflies  14,  115,  195,  205,  253,  255, 
259,  260,  280,  281,  345,  356, 
357,  36o,  361,  368,  370,  372, 
373,  398 

mayfly,  burrowing 255 

mayfly,  howdy 364,  366 

McDonald,  E 62 

McLean,  New  York 350,  352 

Mediterranean  Sea 28 

Melicerta 178,  257,  299 

Melosira in,  112,297,303 

Menyanthes  trifoliata 34  5 

Meridion 1 11,  113,  114,  297 

Merismopaedia 134,  135,  299 

Mesotaenium 119 

metabolism 44,  272 

metamorphosis  195,  197,  200,  201, 
205,  220,  237,  287, 
290 

Metazoa 246 

metazoans 163,  164,  165 

methane 47,48,96 

Micrasterias 52,  53,  119 

microplancton    20 

microscope 15,  101,  115,  327 

Microcystis.  .  .  132,  133,  297,  303,  308 

midge,  net-winged 228,  259,  267 

midges  14,  225,  254,  257,  258,  358, 
.       36i,  371,  373 

migrations 240,  316 

Mikania  scan  dens 345 

milfoils 271,  405 

mink 241 ,  274 

minnow,  red-bellied 294 

minnows  232,  233,  287,  345,  366,  374, 

394,  399 

mites 192,  285 

moccasin  flower 351 

mold  parasites 144 

molds 100 

mollusca,  lotic 373 

molluscs  50,    52,  180,  216,  235,  288, 
342,  345,  352,  382,  390 


molluscs,  shell-bearing 340 

Monostyla    

Moore,  Emmeline 150,  391 

Morgan,  Anna  IT 2<X >,  2  g  ^ 

mosquitoes  227,  280,   2*4,    318,    $39 
346 

moss,   brook-inhabiting 14H 

moss  patches 358 

moss,  xerophytic 351 

mosses i4(,,  ',  (,, 

mossworts i^e 

moth-flies 230,  360 

moth,  tineid 346 

moths 195,  2 is,  2S4/341 

Mougeotia    119 

Mountains,  Rocky no 

mucilage  272 

mucl- 95,  96,  154 

mucus 129,  131.  181 

mud  banks 41,7 

mud   pond 352 

mud  puppy 291 

muscles 256,    2  3 1 

muskellunge . .    313 

muskrat 241,  274,  341,  380 

mussel,   salamander 291 

mussel  shells 216 

mussel,   wash-board 

mussel,   warty-back :m( 

mussels  180,  181,  194,  240,  251.  252, 

254,  257,  286,  2S7.  ; 

290,  291,  292,  324,  332,  341, 

356,  357,  360,  383 

mussels,  eggs  of 2  8  7 

mussels,  fresh- water.  .  .  .  180,  2-2.  286 

Myriophyllum 154,    155 

Mysidacea    

Mysis 189,  190,  301.  3]  1 

Myxophyceae    

Nachtrieb,  H.  F 170 

Naidae    17; 

naiads 152,173 

Nais 15;,.  17;.  177.  321 

Najas 

nauplius [88, 

Navicula t<»>,  i  h>,  11. 

navigation    

necton2i3,  24;,,  294,  296,  31.;.  33*i 
34i 

Necturus 236,  291 

Needham,  John  T 

Nemoura 

Nematodes 17-'.    I  73 


432 


Index 


PAGE 

Nepidae    212 

Netrium    119 

nets,  of  silk  bolting-cloth 18,  20 

Neuroptera 195,  202,  212 

newt,  vermilion-spotted 237 

New  York  State  Museum 165 

nigger-heads 291 

nightshade  bittersweet 345 

Nitella 137.  J38,  139 

nitrates 48,  49,  50,  141 

nitrites 48,  49,  141 

Nitrogen  43,  47,  48,  50,  139,  141,  348, 

351 

nodes 138 

Nostoc 133,282,337 

nostrils    273 

Noteus    299 

Notholca 246,  299,  300,  303 

Notodromas 188,  328 

Notommata  parasita 282 

Notonecta 276,  337 

nucleus 117,  121 

Nymphaea 334 

nymph 201 ,  204 

nymph,  damselfly 208 

"  "  dragonfly .  .  250,  252,  340,  360 

"         Hexagenia    398 

mayfly   278,  340,  341,    369, 

387,    388,    390,    396 

"         stonefly 204,  279 

Obovaria  ellipsis 291 

Odonata 195,  207,  345 

CEdogonium 124,  125,  126 

offsets   272 

oils 273 

Oligochaete 173,  250 

Oocystis 129,  131 

ooze 173,   251 

opcrcula    253 

operculum 182 

Ophiocytium 129,  131 

Ophrydium 161 

orchids 158,  351 

organs,  locomotor 246 

organisms,  chlorophyl-bearing  71 

littoral. 314,  315,  356 

"  lotic  263 

orl  flies 213,  280 

Oscillatoria 109,  133,  245,  297 

osmotic  pressure 245,  272 

osteole 164 

Ostracods.  183, 188,  193,  225,  328,  345 


PAGE 

otter 241,  274 

overflow    87 

oxydation 44,    5 1 

oxygen  43,  44,  45,  47,  48,  72, 
101,  120,  139,  183,  254,  263, 
277,  309,  3".  326,  329,  332, 
339,  345 

oxygen,  consumption  of 44 

"        dissolved    80 

"        excess 44 

"        free 310 

oxylophytes   348 

oysters 379 

Pacific  Ocean 28 

paddle-fish    333 

Palaemonetes 192,  393 

Palmer    48 

Pandorina 103,  104 

Paper  making 381 

Paramecium 160,   165 

Paraponyx 219,  341 

parasites 18,  120,  175,  282,  296 

Parnidae     224 

Parnids  370 

Paulmier 392 

peat 95,  96,  147,  348,  350,  352 

Pectinatella 168,  169,  247 

Pedalion 299,    300 

Pediastrum 123,  245,  299,  303 

Pedicia  albivitta 256 

peeper 236,   237 

Peltandra 157,334 

Peltodytes 223,  224 

Penium  119 

peptones 48 

perch 232,  233,  291,  306 

perch,  yellow 234 

Peridinium 108,    296 

Perla 203, 204 

petioles 271 

Phaeophyceae    135 

Philotria' 155,  156,  228,  319,  321 

Philodina 299,  318 

photomicrographs 117 

photosnythesis .  .26,  28,  29,  45,  46,  71 

Phragmites 343 

Phryganea    34 1 

Physa 182,  337 

pickerel- weed.  156,  157,  321,  334,  405 

pike 231,  232,  233,  235,  387 

pipewort 319 

Pisidium 341,   345 


Index 


433 


PAGE 

pitcher-plant 283,  284,  350,  351 

Pi  tot-tube  current  meter 86 

Placobdella 176 

Plagiola 289,  291 

Plagues  of  Egypt 14 

Planaria    263 

planarians 170,  171 

plancton  18,  20,  28,  45,  48,  49, 
70,  72,  85,  123,  129,  130, 
131,  134,  135,  161,  164,  166, 
185,  189,  194,  235,  243,  294 
295,  296,  299,  300,  301,  302, 
303,  313,  322,  341,  356,  357, 
387,  388,  389,  391,  394 

plancton  animals 299,  301,  325 

Crustacea    391 

entomostraca 393 


feeders 


235 


gatherers 263,  270 

"         local  abundance 306 

"         net 115,  160 

of  open  waters 331 

organisms 248,  296 

"         pulses   305 

shoreward  range 307 

"  of  surface 327 

plancton  strainers 313 

planctonts,  summer    309 

synthetic    308 

Planorbis 155,  182,  337,  345 

plant  assimilation 26 

plant  infusions 160,  165 

plants,  chlorophyl-bearing  .  .  .44,  326 

"      floating 150 

"      insectivorous 282,   283 

submerged 155,  334 

"      transpiration  of 56 

"      vascular.  .  .270,  316,  322,  356 

Platydorina    104 

Platypeza 380 

pleasure  grounds 21 

Plecoptera 195,  203 

Pleurotaenium 119 

pliancy    271 

Ploesoma    299 

plover   239 

Plumatella 166,  167,  169 

plumes 248 

plunge  basins 63 

Podilvmbus    240 

Podophrya 162 

pollen  grains 296 

pollen  tubes Ipl 


_   ,  PAGE 

Polyarthra 25 

Polycystis 

Polycentropus   \aq 

Polygonum 75,34 

Polyphemus 301 

Polytrichium    

Polyzoans 

pond  culture 

pond-dwellers '1  -  2 

pond  at  Lake  Forest,  111 410 

pond,  making  of  a 400 

Pond,  Old  Forge 

Pond,  Parker's 91 

pond-scums    10 1 

pond-snails 327 

pondweed,  ruffled 152,  272 

"        1  sago 326,  3  so,  387 

pondweeds  152,    153,   240,  272,  319, 
321,  334,   352,   39*. 

A  A  4°5 

pondweed  zone 2,^2,  233 

ponds  59,  121,  155,  167,299,  3.7,  316, 
333,  345,  356,  397 

ponds,  hatching 163 

11       inclosed    

Pontederiaceae 156 

Pontederia 157,  3- ; 

pools  14,  57,  64,  81,  133,  156,  163, 
164,  184,  210,  307,  310,  319,  :,22, 
356 

pools,  impermanent    157 

"      polluted 17,; 

"      rainwater 1  B4 

"      stagnant 127,  i/ 

"      temporary 177,  227,  263 

Potamogeton  152,  153,  220,  240,  321, 

334,336,387 

Potentilla 344 

prawn,  freshwater 

prawns 1  \  ■ . 

Precession  of  the  Equinoxes.  . 

precipitation 55 

Priocnemis 

production,  decline  of 

products,  animal  

"         gelatinous 244,   . 

"  metabolic    

"         mucilaginous 245 

prolongations 

propagation 

propagation,  artificial 

propulsion 

propulsion,  caudal 


434 


Index 


PAGE 

Protection  of  breeding  fishes.  .  .  .   385 

proteins 48,  139,  148 

proteins,  liquefaction  of 48 

protoplasm 30,   244 

Protozoa 250,   390 

Protozoa,  parasitic 162 

protozoans  158,   159,    160,    161,   257, 
299 

protozoans,  ciliate 171 

sessile 162 

Psephenus.  .  .  .224,  260,  267,  370,  373 

pseudopodia 159,    162 

Psorophora 284 

Psychoda 359,  360 

Psychodidae 230 

Pteridophytes 149,  150,  151 

Pterodina 299 

pubescence 276 

puddles 316 

pulmonates 337 

punkies 279 

pupa  of  Limnophilus 199 

pupae  of  blackfly 280 

"       dipterous 280 

Pyralidae    218 

Quadrula 289,  291 

Radula 181 

rail,  Sora 239 

"  Virginia 239 

rails 224,    342 

rain   44 

rainfall  55,  56,  57,  69,  74,  77,  88,  316 

rainfall,  excess  of 56 

"        surplus 403 

"        variation  it 70 

rainspouts 166,  177 

rainwater 41,  57,  68 

Rana  pipiens 236 

Ranatra 276,  278,  339 

Ranunculus 156,  321,  334 

rapids    64 

rate  of  streamflow 85 

Rattulus 299 

readaptations 270 

Reaumur 16,  202 

Redi 16 

regions,  arid 57,   75 

limnetic 315,  325,  326 

littoral  315,    325,    326,    341, 

395 
Reighard,  J 28 


PAGE 

relations,  cultural    399 

spatial 326,  331 

Renwick,  Ithaca 15 

reptiles 231,  238 

resemblance,  protective 361 

Reservation,  Clark 63 

reservations,  public 411 

reservoirs 403,  404 

reservoirs  site 403 

respiration    252 

Rhabdoccele 1 70,  172 

Rhichtericlla 129,  131 

Rhizopoda    159 

rhizopods    325 

Rhizosolenia 297 

Rhodophyceae 135 

Rhynchostegium 148 

Riccia 145,  *46,334 

Ricciocarpus 153 

rice,  wild 13,  379,  380,  382 

riffles 64 

rills    77 

Rithrogena 369,   370 

River,  Chippewa 67 

"  Illinois  48,  49,  79,  80,  83, 
85,  103,  107,  131,  171, 
312,  356,  357 

River,  Mississippi 41,  67,  79 

"       Missouri  41 

"       Niagara 61 

"       Seneca 65,  91 

"       Spoon 28,  49 

"       vSt.  Mary's 69 

St.  Mark's    69 

"       Susquehanna 64 

"       Suwannee 94 

riverweeds    1  =52 

Rivularia 133,  134,  297,  337 

rocks,  archacan 52 

rock  ledges 363 

rodents 241,312 

Roesel 16,   202 

rotifers  106,  166,  177,  178,  179,  246, 
248,  250,  257,  266,  269,  282, 
298,  299,  300,  302,  305,  309, 
312,  318,  325,  327,  328,  341, 
390 

rotifers,  loricate 248 

"        resting  eggs  of 325 

"        sessile  332 

Rumex    345 

runners 272 

Ruppia  maritima 71 


Index 


435 


PAGE 

rush,  beaked 351 

"     club  334 

"     spike 354,359 

rushes 89,  157,  38 1 

Ryacophila 370 

Rynchospora    351 

Sagittaria   334 

salamander,  spotted 237 

salamanders.  .236,  237,  291,  337,  379 

Salpina   299 

salts,  mineral 40 

Salvinia 150,  334 

sanitation 21 

Saprolegnia 143,  144 

Saranac  Inn 163 

Sarcodina 1 59 

Sarracenia 284 

Sars 18 

saturation 44,  55 

Scapholeberis 328 

scavengers 18,  175,  282,  283,  296 

Scenedesmus 129,  130 

Sciomyzidae 230 

Scirpus 87,  334 

scuds  183,   189,   190,  332,  341,  345, 
360,  390,  392,  393 

Scutellaria    344 

seals 244 

Secchi'sdisc 27,  28,65,  71 

secretions   257 

sedges 89,  94,  157,  343,  344,  407 

sedges,  tussock 352,  354,  357 

seed  plants 145 

seed  production 272 

seeds  203 

seepage 57,59 

Selenastrum 129,    131 

Sellards 69 

serpents 390 

sewage 140 

sewage  contamination 357 

sewers 1 59 

sheepshead 235,  291,  292 

shelter-building 257,314,340 

shelters.  .258,  260,  294,  326,  372,  395 

shell,  butterfly 291 

"     yellow  sand 291 

shells 244 

shoals30,  73,90,91,145, 156,231,232, 

307,331,333,343 

shore  lines 404,  406,  407 

shore  vegetation 91,  131 


PAGH 

shovels    25(1 

shrimps 183,  1*4,  192 

Sialididae 2 12,  213,  221 

Sialis 214 

Sida 301 

Silica 52,  53,  109,  no 

silt  26,     27,    29,    42,    67,     77,    84, 
85,  191,  251,  252,  254 

silt,  adherent 340 

"    depositions  of 90 

"    excess  of $2(> 

"    inwash  of 

Simocephalus 185,  [fik 

Simuliidae 227 

Simulium  81,  259,  280,  358,  363,  364 

sinks 68,  69 

Siphlonurus  (=  Siphlurus)  205, 

siphons   252 

Sirenia 273 

Sisyra 214,  215 

sludge   17; 

sluiceways 169 

Smith,  Lucy  Wright 204 

snails  180,  181,  216,  227,  254,  260, 
337,  340,  345,  357,  370,  373 
388,  398,  399 

snails,  limpet-shaped    182 

"       operculate 182,  356 

"       pulmonate    [82 

"       viviparous 1 82 

snakes 250 

snipes    239 

societies,  aquatic 294,  296 

bog   348 

lenitic.  .  .315,  316,  356,  360 

11         limnetic 293,  294 

"         littoral 294,  314.  3-- 

lotfc  315,356, 360,362, 
372,  373 

soils,  calcareous 41,  51,  137 

11     siliceous 41 

Solanum  dulcamara 245 

soldier-flies 

solids,  dissolved ; 

"     suspended 41,  43.  54 

solidity 

solutions 

sow-bugs 193 

Sparganium 

spatterdock        154,  3: 
spawning  ground  i 
spawning  time.    . 


436 


Index 


PAGE 

Spelerpes 237,  374 

spermaries    138 

sperm  nuclei 151 

Sphaerella 103,  104 

Sphaeriidae 181 

sphagnum  89,    94,  11 7,  146,  147,  149, 
2*4,348,349,350,351,352, 

353,  355,  359 

Sphenophorus    34^ 

spicules 164,    266 

spiders 183,  192,  346 

spiracles 270,  275,  276 

Spirillum 140 

Spirodela 149,  334 

Spirogyra  119,  120,216,223,263,322 

.  336 

Spirotaenia 119 

Spirulina 133 

sponge  fishers 30 

sponges.  165,  266,  269,  332,  335,  341 
sponges,  fresh-water  164,     265,     266, 
325 

sponges,   marine 266 

spongilla  flies 214,280 

sporangia    143 

spore  development 310 

spores 140,  142,  296 

springs 53,  57,  59,  64,  84,  152 

springtails 195,  338 

stagnation 35,  39 

starches 244 

statoblasts  164,  165,  169,  247,  265, 
266,  269,  325 

Staurastrum 51,  119,  299 

Stauroneis Ill 

Stenostomum 170 

Stentor 160,332 

Stephanoceros 178,  299 

Stephanodiscus .  .  .  .  in,  1 12,  114,  297 

Steuer 27 

Sticklebacks 234,  235 

Stokes,  Alfred  C 19 

stomates 151,  270,  271 

stoneflies  195,  203,  259,  278,  280,  345, 

360,  368,  374 
stoneworts  50,   52, 101, 137, 138,  139, 
251,263,319,334 

strainers 252,  253,  365 

strata,  soluble 68 

stratification,  horizontal 307 

thermal  31,  34,  35,  39, 
46,54,71 
Stratiomyia    338 


PAGE 

stream-line  form  249,  250,  251,  259, 

273,  274,  3U,  366 

streams.  .  .  .59,  77,  141,  231,  319,  406 

streams,  pollution  of 80,  130 

Streptothrix  142 

Strodtmann    305 

sturgeon,  shovel-nosed 235 

sturgeon 291,333,356 

Stylaria 173 

suckers 232,  233,  234,  259 

sulfur 53 

sundew 156,  283,  351 

sunfish 232,  233,  234,  388 

Surber 289 

surface  film 181,  327,  328,  337 

swale-flies 230,  277,  329,  346 

swales 56,  64 

Swammerdam 16,  202 

Swamp,  Dismal 90 

Okefenokee 93 

swamps,  coniferous 1 52 

"  marine 90 

sweet  flag 157,  343 

swimmerets    192 

symbiosis 282 

Symphynota 287 

Synchaeta 178,  299,  300,  303 

Synedra 1 11,  112,  297 

Synura 103,  107,  303 

Syrphidae 229 

syrphus  flies 339,  380 

Tabelaria  in,  114,  115,  245,  297,  303, 

305 

Tabanidae    227 

tadpoles    236 

tailfin 251 

Tanypus 225 

Tanytarsus 257,  371,  372 

tardigrade 164 

tear-thumb 343,  344 

teeth,  raptorial 235,  313 

temperature  25,     37,  244,  248,  304, 

306,  307,  308 
temperature,  at  different  depths 

32,  34,  35,  36,  38 

changes  of 40 

conditions  of .  .32,  36,  46 

fluctuations  of 345 

"  levels  of 39 

"  optimum 131 

range  of 33,  34 

"  yearly  cycle  of 34 


Index 


437 


PACK 

tentacles 176 

terns    342 

Tetmemorus 119 

Tetrapedia 130, 299 

Tetraspora 129,  131 

thallus 153 

thermocline 37,  39,  72,  309,  311 

thoracic  appendages .  ...  183,  188,  189 

Thysanura   195 

Tipulidae    297 

Tipula 360 

tides 73 

toads 236,   237 

Taeniopteryx 279 

topography 74 

trachea   275 

tracheae 270,  278,  279 

Trachelomonas 103,  108 

tracheoles 278,   279 

transpiration    3-1 8 

Trembly 16 

Triaenodes 215,  218,  280,  337 

Triarthra 299,  300 

Tribonema 124,  126 

Trichobacteria 141,    142 

Trichodesmium 101 

Trichoptera 195,  214 

trochophores    250 

Trochosphaera 178 

trout 163,  176, 313,  385,  393,  394 

trumpets,  respiratory 277,280 

tubercles 256 

tube-dwellers 37° 

tubes 121,  226,  240,  278,  372 

tubers 272,  380,  382 

Tubifex 173,  174,  254,  340 

turtles 175,  238,  343,  390 

tusks,  mandibular 255,  256 

Typhaceae   156 

Typha 91,  321,  334,  346 

Ulothrix 124,  336 

Unio 181,  323,  324 

Urodela 236 

Uroglena 295 

Utricularia 117,  i55,284,  285 

Vacuoles 3 IO 

Vallisneria 153,  240 

valves 109,  252,  273,  288 

vapor 55 

vaporization 4° 

Vaucheria 121 


PAGE 

vegetable  forage 399 

vegetative  propagation 272 

ventral  suckers 367 

vertebrates 239,  37  | 

Volvox.  .  .  101,  104,  105,  245,  282,  337 
Vorticella 161,  295,  299 

Ward,  H.  B 28,  312 

waste  wet  lands 401,402,407 

water-boatman 201,  211,  276 

water-birds 239,  240 

water-bloom  14,  15,  101,  104,  106, 
129,  132,  133,  161,  295, 
296,  299 

water-borne  diseases 21 

water-bugs 195,210,276,318 

water-content 26 

water-cress 145 

water  crops yj2,  403 

water  crowfoot 156,  319,  344 

water  culture  377,  378,  379,  391 ,  400 
401,402,403,404,406, 
409 

waterfalls 64,  80,  81,  1 17,  358 

water-fern 134,  145,  I49i  33  I 

water-fleas  19, 185,  186,  246,  247,  248, 
249,  266, 267,26c),  285,  300, 
327,328,.387.390t39l.392 

waterfowl 9I,239,3,So>  4°9 

water-garden 378,404,  407,  409 

water-glass 409 

water  hemlock 345 

water  horn  wort 319 

water-lily 154,  334,  382,  404 

water-meadows 153,  401') 

water  milfoil 154, 155,  319 

water-mites 193,  194,  301 

water  mold 140,  143,  144 

water  mosses 140,  148 

water-net 122,  123 

water-penny 224,  2<>o,  36s 

water-plantain ^24,  345 

water  plants too 

water  power 4°3 

water  purslane 156 

water  reservoirs.  .  .  169,  349,  401,  402 

water-scorpion 212 

water-shamrock 140,  405,  407 

water  shield 154.  334,  4°- 

water-skaters 

water  snakes 

water-striders 

water  table 5 


438 


Index 


PAGE 

water-tiger 280 

water-vole 273 

water  walking-stick 276 

water  weeds.  .  .156,  161,  190,232,392 

water,  buoyancy   of 3° 

densitv  of  .30,  31,  36,  54.  3 14 

depth  of 29,307,321 

for  drinking 21 

fertility  of 56 

force  of 135 

freezing  of 31,  80 

ground 30,  56 

hardness  of 51 

high  and  low 74.  9° 

mineral  content  of 52,  53 

mobility   of 3° 

population  of 100 

run-off 56,  57,  85,  117 

running 39 

as  a  solvent 25,  40 

stagnant 13° 

standing 44 

storage  of 4°3 

surface  tension  of 54 

thermal  conservation  of  40,  79 
transparency  of .  .  .  26,  308,  309 

turbidity  of 27 

underground  channels  of .      70 
viscosity  of  30,    54,    244,    248, 
249 

wastage  of 403,  404 

waters,  alkaline 51 

cave 191 

drainage    48 

flood 42 


PAGE 

waters,  mineralized -40 

polluted 162 

"         public 386,  400 

Weismann 301 

wells    191 

Wesenberg-Lund 248 

whales 19,  274,  275 

Whipple,  G.  C 27,  42,  401 

whitefish.  ...   231,  233,  313,  388,  393 

wiers    169 

Will-o'-thewisp 96 

willows    158 

Wilson,  W.  M 79 

winds 27,  33,  35,  85 

Wolffia    15° 

Wolle in 

worms 254,  257,  285,  367,  390 

worms,  cylindric    172 

hair    174 

Nematode 172 

Nemertine 174 

oligochete 325 

parasitic    174 

thread 172 

true    34° 

wrigglers 227,  250,  339 

Wright,  A.  H 236,  237 

Zaitha  211 

Zannichcllia. 153 

zooids    166,  169 

Zostera    334 

Zygnema 119 

zygospores 120,  263 


ERRATA 


PAGE 

19     line  4,  for  Connecticut  read  New  Jersey 

33     line  2,  for  effect  read  affect;  line  4,  for   procession  read  precession. 
97     last  line,  for  club  rush  read  spike  rush. 
103     at  end  after  Ceratium  add,  (figure  reversed  in  copying). 
127     line  4,  for  form  read  forms. 

head  line,  for  Tetranspora  read  Blue-green  Algae. 

line  14,  for  dessicated  read  desiccated. 

line  12,  for  Relicit  read  Relict. 

heading,  for  Lymph  read  Nymph. 

line  12,  for  p.  280  read  p.  279. 

line  1,  for  p.  359  read  p.  360. 

line  18,  for  keep  it  long  afloat  read  insure  that  it  will  float. 

line  31,  for  fig.  134  on  p    226  read  fig.  223  on  p.  373. 

line  27,  for  Siphlurus  read  Siphlonurus. 

line  5,  for  season  read  period. 

line  18,  for  Hibenaculea  read  Hibernacula. 

line  28,  for  fifty  read  twenty;  line  29,  for  59  and  100  read  SO  and  60. 

in  legend  to  fig.  201  for  tigrinum  read  punctatum. 

line  1,  for  eaves  read  leaves. 

line  6,  for  Siphlurus  read  Siphlonurus. 

add  in  proper  order  this  line: 

Page  292.     A  Bed  of  Pickerel  Weed. 

fig.  178  with  legend  reprinted  below: 


43 8  Index 

PAGE 

water-tiger 280       waters 


: 


:£;*■ 


' 


ill 


■I 


ii 


■ 


